FUNCTIONAL ANATOMY OF THE MAMMAL

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1 McGRAW-HILL PUBLICATIONS IN THE ZOOLOGICAL SCIENCES A. Franklin Shull, CONSULTING EDITOR FUNCTIONAL ANATOMY OF THE MAMMAL

2 SELECTED TITLES FROM McGRAW-HILL PUBLICATIONS IN TH~ ZOOLOGICAL SCIENCES A. Franklin Shull, CONSULTING EDITOR' Baitsell HUMAN BIOLOGY, Breland MANUAL OF COMPARATIVE ANATO;\IY Burlingame HEREDITY AND SOCIAL PROBLEMS Chapman ANIMAL ECOLOGY Clausen " ENTOMOPHAGOUS INSECTS Frost GENERAL ENTOMOLOGY Goldschmidt PHYSIOLOGICAL GENETICS Haupt FUNDAMENTALS OF BIOLOGY Hyman THE INVERTEBRATES: PROTOZOA THROUGH CTENOPHORA Johannsen and Butt EMBRYOLOGY OF INSECTS AND MYRIAPODS Leach FUNCTIONAL ANATUMY OF THE MAMMAL Mitchell GENERAL PHYSIOLOGY Mitchell and Taylor LABORATORY MANUAL OF GENERAL l)hysiology Pearse ANIMAL ECOLOGY Rogers TEXTBOOK OF COMPARATIVE PHYSIOLOGY Shull EVOLUTION LABORATORY OUTLINES IN COMPARATIVE PHYSIOLOGY HEREDITY PRI;-;CIPLES, OF ANIMAL BIOLOGY Shull, LaRue, and Ruthven PRINCIPLES OF ANIMAL BIOLOGY Simpson and Roe' QUANTITATIVE ZOOLOGY Snodgrass PRINCIPLES OF INSECT MORPHOLOGY Storer GENERAL ZOOLOGY LABORATORY MANUAL FOR GENERAL ZOOLOGY Van Cleave' INVERTEBRATE ZOOLOGY Welch LIMNOLOGY Wolcott ANIMAL BIOLOGY There are also the related series of M Graw-Hill Publications in the Botanical Sciences, of which Edmund W. Sinn,:,tt is Consulting Edito~, and in the Agricultui'q.l Sciences, I of which Leon ]. Cole is Consultin~ Editor.

3 FUNCTIONAL ANAT~ OF THE MAMM~ A Guide to the Dissection of the Cat and an Introduction to the Structural and Functional Relationship Between the Cat and Man by W. James Leach. ASSISTANT PROFESSOR OF BIOLOGY TEMPLE UNIVERSITY First Edition McGRAW-HILL BOOK COMPANY, INC. New York and London 1946!'his 18 trom. 'Cotbari Book OeDot. 8.MBAY. 12

4 FUNCTIONAL ANATOMY OF THE MAMMAL Copyright, 1946, by the McGraw-Hill Book Company, Inc. PRINTED IN THE UNITED STATES OF AMERICA All rights reserved. This book, or parts thereof, may not be reproduced in any form without permission of the publishers. The quality of the materials used in the manufacture of this book is governed by continued postwar shortages.

5 PREFACE THIS BOOK is intended for students who are beginning work in anatomy and has been planned to meet the requirements of various curriculums. Special attention has been given to th needs of students of anatomy in educational field's, particularly in nursing, health, and physical education, where opportunity to do human dissection may be la;cking or limited.. Such considerations are also of value in liberal arts courses of a premedical character. Therefore, the material has been s~lected to substantially supplement courses in human anatomy (and phy"iology); to serve as the mammalian portion of courses in comparative vertebrate anatomy; or to be used in courses principally concerned with g~neral mammalian features. The presentation is designed to integrate a rtj-ther specific laboratory study of the cat with text material of a more gerleral character with emphasis on man. As far as possible, descriptive avatomy has been treated with special reference to the functional organization of the parts and their interrelationships. In this, connection, functional anatomy gives emphasis to the manner in which the parts work together rather than with how each of the parts is constructed as a separate unit. However, a comprehensive view of anatomy must be based upon the observable details, and considerable preliminary description seems necessary in presenting an understandable treatment of functional relationships. Text material in anatomy is really intelligible only when studied in. connection \vith actual dissection, or after much laboratory experience has been acquired. For this reason, the practice of substituting a quadruped mammal for man is a common laboratory ptoc~dure in many courses which do not include human dissection. There can be but little doubt that the practice is very helpful, but it also presents many difficulties to the average student. One of the principal aims of this book is to consider the relationships between quadruped mammals jl.nd man and to discuss them in some detail. The modifications of structure, which have accompanied the assumption of the erect posture in man, would appear to deserve much more consideration than has been given to them in usual comparative anatomy courses. Certain specific conditions in the cat, however, have been especially emphasized because of its common use in experii1lental physiology, pharmacology, and as a subject for veterinary practice. Many medical school students who have had work in mammalian anatomy appear poorly prepared for experimental studies on mammals bec:,j.use their attention had not been directed early to the application of JIlammalian anatomy to physiologic investi)l!;ations. Other considerations have been drawn to the attention of the student to stimulate his interest in the cat as an animal from which much other practical information can be obtained. v

6 VI PREFACE Some tabulated material included in the text has been modified from unpublished outlines prepared by Professor J. Percy Moore of the University of Pennsylvania. The author is also indebted to' Professor Moore for many suggestions on the functional treatment of anatomy. The author greatly appreciates the helpful advice and criticism of present and former colleagues and students. Particular mention is made of the help of Profs. M. L. Leitch, M. F. Keen, and O. G. Rybachok, who hav.e used an earlier form of the book in their classes and have called the author's attention to many matters-requiring correction. Other helpful advice has been contributed by Prof. A. A. Schaeffer, chairman of the Biology Department in Temple University. The' author is particularly indebted to W. B. Strickland who has copied and relettered the original figures and assisted with the modification of figures from l\livart. Publishers and authors have been most generous in granting permission for use of other figures and the author wishes to express his thanks here to W.. B. Saunders Company, Charles Scribner's Sons, The C. V. Mosby Company, Medical Publishers, and Lea & Febiger. Acknowledgment is also due S. H. Camp and Company for permission to use four figures by Tom Jones, which are reproduced from his "Anatomical Studies, for Physicians and Surgeons." Many of my students have contributed much to figures in the present work. Special mention is made of assistance given by Earl Kvam on the drawings of the muscular system. For terminology and pronunciation, the author has relied principally on Dorland's "Medical Dictionary." For reference to the descriptive anatomy of the cat, Reighard and Jennings, "Anatomy of the Cat," has been most helpful. PHILADELPHIA, PA.,. October, W. JAMES LEACH.

7 PREFACE. CONTENTS' Chapter I GENERAL CONSIDERATIONS 1 Terms and definitions. The principle of homology. Divi~ions of structural organization. Anatomical position and posture. Characteristics and classification of mammals. Anomalous and vestigial structures. Chapter II THE SKELETAL SYSTEM Functions and divisions of the skeleton. Terms used in describing bones. The mammalian skull. Skeleton of the cat. Articulations and lever systems. Chapter III SUPERFICIAL DISSECTION OF THE CAT 59 Superficial characters and landmarks. Dissection of the skin. Fascia, cutaneous nerves, and blood vessels. Chapter IV A STUDY OF THE VOLUNTARY MUSCLES. 67 Structural and functional features of a skeletal muscle. Anatomical position and muscle actions. A practical study of muscle actions in man. :Method of muscle dissection. Functional anatomy of the principal muscles of the cat. Special modification of muscles in man. Study list of muscular activities. Chapter V A SURVEY OF INTERNAL ANATOMY 111 Sectional aspects of the head and pharynx. Body cavities, membranes, and general visceral arrangements. Innervation of the viscera. Practical problems on internal anatomy. v Chapter VI THE ALIMENTARY SYSTEM... The alimentary canal. Glandular derivatives of the canal. Chapter VII ) THE RESPIRATORY SYSTEM The course of respiratory air. General features of the lungs. vii

8 Vlll CONTENTS Chapter VII I THE VASCULAR SYSTEM The heart and main vessels. Systemic veinf'i. Systemic arteries. Anomalies of the vascular system. Circulation before birth. Lymph vessels and nodes. General discussion and problems. Chapter IX THE UROGENI,TAL SYSTEM... The reproductive system. Nephric system. THE NERVOUS SYSTEM Chapter X General features 01 the brain and cranial nerves. The brain 01 the cat. The cranial nerves. Spinal cord and nerves. The brachial nerve plexus. Sacral and lumbal' plexi. Autonomic division. General discussion. Chapter XI SPECIAL SENSORY APPARATUS Unique character of special sense organs. The functional anatomy of the eye. The hearing apparatus. Chapter XII THE ENDOCRINE ORGANS.... A summary and discussion. Appendix LABORATORY PREPARATION AND DISSECTION MATERIALS... :" PRES,ERVATION OF Skeletal material preparation. Staining fetal animals for a study of bone formation. INDEX '. j l

9 Chapter I GENERAL CONSIDERATIONS A CONSIDERABLE part of the material in the following chapters deals with the structure of the common domestic cat. Many students properly ask why the cat is so commonly studied in mammalian anatomy courses rather than some other type of mammal. Some of the reasons for the use of the cat as laboratory material are easily explained. The cat is of convenient size for laboratory work: it is large enough to allow for clear observation in dissection. Strays and unwanted specimens are fairly numerous and easily obtained. In large cities, thousands of cats are collected each year by city pounds and humane societies. From these sources, biological supply companies obtain the bodies in considerable numbers and at reasonable prices. But these advantages are really not so important from the biological standpoint as is the position of the cat with reference to mammals in general. In a classification of all mammals, organized on a basis of structural specialization, the cat occupies a position near the middle of the list. This means that the cat may be used as a fairly representative type of the class as a whole. From the purely structural standpoint, man is not far removed from the position of the cat in the mammalian scale. This does not mean, however, that the cat is most nearly like man of all mammals. Apes and monkeys are obviously more similar, but they are not so readily available for laboratory study. Rabbits, rats, and fetal pigs are other mammals that are often used in general mammalian studies. But these forms are commonly regarded as being more highly specialized structurally than either man or the cat. Terminology and methods learned in the dissection of the cat are readily applicable to the human body. For most students, the principal value of mammalian dissection is in making anatomical terms really intelligible. Textbook anatomy has little real meaning unless the student can visualize structures as they actually occur in the body. Proper visualization of structure is learned only by laboratory observations. Therefore, it is of utmost importance for the student to learn anatomical terms with direct application and reference to the body, not merely as words in a textbook. Throughout the dissection of the cat, the student should attempt to understand the relationship of structures observed with those of his own body. 1

11 GENERAL CONSIDERATIONS 3 its marrow is centrally located. The cavity of a tubular structure is frequently referred to as its lumen (pi. lumina). Any constant and conspicuous point on a body serves as an anatomical landmark. Less prominent landmarks may be located by descriptions of direction and position from conspicuous points. Body regions are described from locations of landmarks, as are the lines of incision in dissection. or surgery. B,my landmarks that may be seen superficially or felt (palpated) are important in describing less conspicuous or discernible areas. ~ Dissection refers to intentional systematic separation or division (not necessarily cutting) of the parts of an organism to expose new aspects and relationships to view. This involves precise techniques and close observation since the anatomy is learned during the process of dissection as well as after the dissection is completed. Structures under dissection should be considered as integrated parts of a living body, not as isolated elements of a dead one. Gross anatomy is concerned with the more obvious aspects of form, structure, and organization as exposed and studied without the microscope. Histology refers to microscopic anatomy and requires the use of specially prepared sections of tissues or the use of microdissection technique on living tissue. Cytology deals wit~ the details of cellular anatomy and merges closely with cellular physiology, genetics, and embryology. Embryology deals with the development of the individual structurally and physiologically. Specialized branches of descriptive anatomy are usually treated as follows: osteology, the anatomy of the bony framework; neurology, the nervous system; myology, the muscular system; cardiology, the heart and blood vessels; splanchnology, the alimentary canal. Anatomical terms and the specific names given to anatomical parts are mostly Latin and, when properly translated, are usually descriptive of the parts. The human body was described by early anatomists before most other forms had been described in as much detail. Similar parts of other organisms were later given the names first applied to man. This system of establishing a terminology for similar parts, in different animals, has been carried through to the lower vertebrates upon the assumption of structural relationships and common ancestry. Fundamental similarities in structural features and organization exist from fish to man. Physiology is related to anatomy in that it is based upon the chemistry and physics of living protoplasm, while anatomy is limited to the visible structural organization through which physiological activity is expressed. A study of the mechani~al arrangement of the bones, the attachments of muscles, the nerve connections, and the blood supply and drainage of various organs are all,parts of anatomy. The mechanical actions of the arm as a functional unit could be readily ascertained by a study of its structural organization in a dead body. But the chemistry and physics of

12 6 FUNCTIONAL ANATOMY OF THE MAMMAL thorax possess attachments for ribs ; etc. Thus, if one knows the structure of anyone such segment, this knowledge serves as a basis for an understanding of similar segments. Ribs and spinal nerves are also serially arranged. But the adults of mammals do not exhibit the original FIG exual homologies in the external genitalia of man. A, external genitalia of an embryo of 16.8 mm., showing the genital tubercle from below; B, external genitalia of a male embryo of 45 mm.; C, external genitalia of female embryo of 49 mm. (After Spaulding.) A, anus; A.P., anal pit, at the bottom of which lies the anal portion of the cloacal membrane; A.T., a nal tubercle; E.T., epithelial tag, which later disappears; G, glans of penis and clitoris; G.P., gluteal fold; L.S.S., la bioscrotal swellings; R, raphe; S, shaft of penis and clio toris; T, tail ; U.F., urethral fold; U.G., urethral groove; U.O., urogenital opening. (From W eiman, "Vertebrate Embryology."). segmental arrangement of parts superficially. Developmental stages in all Vertebrata are conspicuously segmented. The remarkable serial homology between the fore and hind limb of animals is obscured by the modifications of use, but the similarities even here are striking as to fundamental structural organization and arrangement of the parts. Sexual homologies. In both the male and female of any species the embryonic development of sexual parts is begun on a similar architectural

13 GENERAL CONSIDERATIONS 7 pattern. For some time, no clear structural difference between sexes is obvious. Following this indifferent period, however, a striking differentiation occurs which leads to a specialized condition of maleness in some and to the less specialized femaleness in others. Abnormal development sometimes occurs so that some sexual structures (genitalia) in an individual assume a male character while other sex structures, in the same individual, assume femaleness. This unusual or anomalous condition is called pseudohermaphroditism. It is not analogous or functionally similar to true hermaphroditism. Complete bisexuality does not occur in mammals. Some incomplete duplication of sexual parts, however, has been reported for man as rare anomalies. In these, partial development of both ovaries and testes in the same individual have been reported to occur. External genitalia are most commonly affected. A fourth type of homology occurs within the serially homologous appendages. This may be described as a radial distribution of similar parts. Radial homology is best illustrated by an examination of the hand. For example, the fingers tend to radiate from the wrist, and each possesses serially distributed phalanges. The bones of the wrist and hand tend to radiate from the two bones of the lower arm, and these two bones.are extensions from the single bone of the upper arm. The bones of one digit are not only similar to each other, but also to the bones of any other digit. Five digits represent the generalized condition, and deviations from this number are considered as specializations. The single digit of the horse therefore represents a highly spe~lized condition. DIVISIONS OF STRUCTURAL ORGANIZATION The cell is considered the basic unit of structure.aince it is the smallest division of a body having an apparent organization with respect to the general functions. These general or basic biologic functions concern growth~ reproduction, metabolism, sensitivity, and motility. With the differentiation of cells, from a generalized embryonic condition, various types of cells are formed. The numerous cells of a common type become associated in the performance of a special duty within the larger organization. A tissue consists of a number of similar cells and their intercellular elements associated together to perform a rather specific function. In general, any cell within any type of tissue can perform all the basic biologic functions, except, perhaps, division or reproduction in some types. The closely associated similar cells forming a tissue become highly specialized in one direction only, however. For example, muscular tissue or the cells forming the bulk of a skeletal muscle are especially adapted for contraction, "whereas the protoplasm of other types of cells is only slightly contractile. Nervotis tissue is particularly sensitive and especially adapted to detect various stimuli and transmit impulses; yet all cells are somewlj.at

14 8 FUNCTIONAL ANATOMY OF THE MAMMAL sensitive in their physiologic character to their environment and the changes therein. It is said that no new nerve or 1~~ cle cells are formed in man after birth; growth in these tissues is dependent on an increase in size of existing cells rather than in reproduction of new o~es. Types of tissues Various classifications of the body tissues have been proposed. For our purposes, we may regard the tissues as comprising five fundamental types. These are epithehal, connective, muscular, nervous, and vascular. Numerous subtypes of the fundamental kinds occur. Epithelial tissues are first recognized by their position in covering free surfaces and as lining cavities. In genera, the lining of cavities that open to the outside possess numerous mucous cells and are known as mucous membranes or mucous epithelium. The thin rnembranous lining of the body cavity and the covering of viscera secretes a thin watery l:1uid resem'oymg 'o\ood seruin, and these membranes are known as serous epithelium. The retina of the eye and specialized parts of other A sense organs form nervous epithelium; the surface of the ovary and the lining of the tubules of the B FIG. l.4.-the secretory function in epithelial cells. A, cells of such a gland as the salivary glands or pancreas, showing zymogen granules accumulated in the part of the cell adjacent to the lumen, or cavity, of the gland. B, two goblet cells from the intestine of a vertebrate, showing the accumulation of mucus and its extrusion into the lumen of the intestine. (From Wolcott, "Animal Biolooy.") testes form germinal epithelium. Glands that possess ducts are IJlade up largely of glandular epithelium. The epidermal layer of the skin is, of course, epithelium and possesses several layers, or strata. Connective tissues are most readily characterized by their intercellular elements, which are formed by the cells and which usually separate them widely. These products of connective-tissue cells perform the functions of support, connection, and protection. Examples of subtypes are: bone, cartilage, tendons, ligaments, fascia, and fat. The living protoplasm of connective tissues is usually very scant compared with the abundance of the nonliving intercellular materials or matrix, and the cells are relatively inactive in the actual performance of connective-tissue functions. Muscular tissue is composed of elongated cells that are structurally and functionally adapted for contraction. Three types occur: skeletal, cardiac, and smooth: Skeletal muscle is under conscious control (voluntary) and makes up the bulk of the body. Cardiac muscle is found only in the heart. It has some histologic resemblance to )skeletal muscle but differs fundamentally in that the cells are interconnected and not activated

15 GENERAL CONSIDERATIONS 9 A s c FIG Different typcs of muscle cells. A, portion of.a striated muscle fiber, showing a section in which the contractile fibrils are divided into groups by semifluid sarcoplasm. Two nuclei are shown, surrounded by undifferentiated cytoplasm, and the whole fiber is surrounded with a delicate sheath, or sarcolemma. B, three nonstriated muscle fibers, or cells. C, several cardiac muscle cells. All highly magnified. (From Wolcott, "Animal Biology.") Hoverskrncanal FIG Different t~es of connective tissues; solbewhat diagrammatic. A, bone, showing the Haversian canjis, which transmit the blood vessels and nerves, and the lacunae, which lodge the bone cells, or bone corpuscles. B, Portion of subcutaneous areolar connective tissue, shoy.ing several tissue elements. C, fat. D, tendon in longitudinal ' section, showing longitudinal fiba bundles and rows of cells crowded int.o the space between them. E, section of cartilage with the cells lodged in spaces in the chondrin. All highly magnified. (From WolcoU, "Animal Biology.")

16 10 FUNCTIONAL ANATOMY OF THE MAMMAL by voluntary conscious control. The smooth musculature of the body is distributed among many organs. Like cardiac muscle, it is involuntary, but the fibers tend to be separate units and are spindle-shaped. The name is derived from the absence of transverse striations, wh~h appear in the fibers of skeletal and cardiac muscle when examined microscopically. Smooth muscle is abundant, particularly along the alimentary canal and urogenital tract. The cells also are numerous in small arteries, where they serve to constrict these vessels and cause changes in the distribution of the blood to the various parts of the body. This constricting action is seen in paleness; whereas extreme dilation produces a flushed appearance. Nervous tissue is highly specialized for the reception, transmission, and coordination of stimuli. The morphology of the cell types is indicative of their particular function: sensory, motor, or associative. In the central nervous system, the nerve tissue is supported by a specialized connective tissue consisting of neuroglia. Processes of nerve cells may be extremely long. A nerve consists of these elongated processes of cell bodies. Vascular tissue consists of the elements of blood and lymph, both liquid parts and formed bodies (corpuscles and platelets). Included in this type by some authors are lymph nodes, the. spleen, and the blood-forming tissues such as red bone marrow. Some authorities consider the vascular tissues as one of the connective-tissue types. In the blood and lymph, the cells are separated by an abundant liquid intercellular part, the plasma. Organs The organized association of various types of tissues in the performance of a broader function than that of a single tissue constitutes an organ. In many instances, an organ possesses one or more types of each of the five fundamental kinds of tissues, one of which is dominant, the others being supplementary. Thus, the tissues necessary to make the stomach a functional organ in the alimentation of food may be cited as follows: (1) epithelial of two general types (serous and mucous), (2) muscular of the smooth type, (3) connective, binding the other types together. In a more minute analysis we would also find (4) vascular tissue and (5) nervous tissue which, respectively, nourish and help regulate the organ. The essential digestive function is performed by the dominant secretory mucosa, but obviously the other types are necessary and contribute to the digestive and alimentary function of the organ as a whole. Systems A series of associated organs, usually, but not necessarily, anatomically connected with each other make up a system. The alimentary system may be used as an example of a system of anatomically associated organs that function in the alimentation of food. Each or!;,'an along the canal has a rather specialized function in the general function of the system.

17 GENERAL CONSIDERATIONS 11 Thus an organ is less specialized than a tissue but more specialized than a system to which it belongs. The ductless glands are organs that make up a physiological system. Parts of this system are anatomically associated with other systems, and most of the several glands are anatomically isolated from each other and show no structural continuity with each other to indicate functional associations. Even tcye skeletal muscular system lacks obvious continuity of its parts, and in considering the various joints over which muscles work, they are better understood as making up coordinated s:tries of similarly acting systems. Thus, we must say that a system is an association of organs of a close structural or functional relationship. These are arbitrarily classified on the basis of the similarity of the parts in contributing to a common function. The close interassociation of the systems constitutes the organism. The unity of the organism, as a whole, is fundamental. An understanding of how the systems work together is the aim of determining their separate structures. A classification of the systems The systems are classified in various ways. The following will serve our purpose in analyzing these with relation to function. The order given is applicable in an orderly study of systematic functional anatomy, and this order will be followed except where sectional considerations are interposed. Integumental. The skin with its derivatives forms the integument. It is the most generalized of the systems from the functional standpoint because of its varied and overlapping functions, which include protection, temperature regulation, and milk production in the female. Skeletal. Connective and supporting tissues make up the skeletal system. In a broad sense, it comprises both the gross and microscopic framework of the body. The bony skeleton is only a part of this system. Muscular. This system is made up of the skeletal musculature of the body which has to do with the motive power in motion and locomotion. It is unique in being controlled by volition, or will. Alimentary. The term "alimentary" is used here rather than "digestive" since the system is not only concerned with the digestion of food, but also with the elimination of the wastes of digestion. Vascular. The vascular system includes the muscular heart and the blood and lymph channels. In a more detailed sense, it includes the structure of the fluids. Structures that give rise to blood cells may also be considered in this category. Respiratory. In this system are considered the parts over which air passes. These parts are concerned with exahange of gases from the blood to the outside air. Although this system is anatomically associated with the food canal, it is functionally more closely related to the blood stream.

18 12 FUNCTIONAL ANATOMY OF THE MAMMAL Genitourinary. The genital and urinary systems are ltlually treated together since the wastes of kidney excretion pass through outlets common to the genital apparatus. In embryology and comparative anatomy, they are closely associated in origin and gross function. Nervous. The comparatively rapid regulation and coordination of body activities are achieved through the mechanism of this system. Its function is to detect, transmit, and coordinate various stimuli. Endocrine. The ductless glands are functionally connected by means of the blood stre1,m. They secrete hormones, which are chemical regula~ tors of body activities and which induce activity of a more persistent character than is generally common to the nervous system. Many of these glands seem closely interdependent upon each other functionally. It is obvious that any attempt to treat anatomy entirely through the study of the systems presents a great many difficulties. Recognition of physiologic systems tends to emphasize these difficulties. Yet the complexities belong to the organism, and no simple method is yet available for an understanding of living things. THE ANATOMICAL POSITION AND POSTURE. In describing movements of the appendages or shifts in position of parts of the body, it is necessary to assume a definite starting point. Muscle action, for example, is described for the human with the body standing erect, the arms hanging at the sides, and the palms facing forward. The terminology used in describing muscle action for the cat has been adapted from the descriptions given for man. This has resulted in considerable confusion, since the anatomical position for describing man would be impossible for the cat to assume under natural conditions. The appendages of the Vertebrata primitively arose as lateral extensions, i.e., paired fins of fish, which act as stabilizers while the body is supported by water. The primitive tetrapods (aquatic salamanders) use the appendages for limited support and creeping locomotion. In most quadruped mammals, the body is carried comparatively high from the ground. To achieve the advanced quadruped position, a rotation of 90 degrees in each limb has occurred, which brings the limbs ventrally to their present position under the body. The forelimb has rotated caudally to bring the original dorsal surface of the appendage to face backward and to allow the elbow to be directed dorsocaudad. To prevent the digits from pointing backward, an additional torsion of the appendage occurs to bring them around to the front. In accomplishing this, the ulna and radius of the forearm become crossed and the forearm assumes a prone position. In most mammals, the forelimb is fairly well fixed in this position. In man, the crossing of the two bones can be felt in the forearm in moving the hand from a "palm-up" to a "palm-down" condition. A forward rotation from the primitive condition has occurred in the hind limb,

20 14 FUNCTIONAL ANATOMY OF THE MAMMAL its beginning during a tree-inhabiting period. Both hands and fee~pparently became grasping organs during this arboreal period. But the hands became so highly specialized as graspers that their further use in walking was largely lost. The return to the ground of man's ancestors also occurred with the feet poorly designed to support the entire weight of the body. Many other changes also have occurred in the structural character of man, apparently during his arboreal era: the body flattened dorsoventrally, instead of bilaterally; the collar bone (clavicle) becam~ strengthened to serve as a cross~brace between the breast bone (sternum) and shoulder (scapula); the arms became more free of the trunk to move in wider ranges; and the eyes moved to a more forward position, permitting better bifocal vision. The erect posture, however, resulted in a sagging of the viscera and a change in the original curvature of the spinal column. Rupture (hernia) and back sprain are common to man. The upper part of the body rests heavily on the sacral vertebrae, which form a triangular wedge between the hip bones. Because of the faulty architectural design of the union of the sacrum and pelvic girdle, falls and jars often result in sacro-iliac difficulties. Among other defects that may be attributed to our arboreal ancestry are the poorly designed supporting arches of the feet and the partly degenerate little toe. Shoulder injuries are also common to man because much of the original strength of the joint has been sacrificed in gaining freer movement for it. Modifications of structure appear to follow modifications of their functional circumstances, and vice versa. While the posture of the cat in relation to the ground is more primitive than the erect posture of man, relatively more muscles are required to maintain it and to function in locomotion. Since both cat and man use the hind legs for locomotion, there is less difference in the pelvic limbs of these forms than in the front appendages. In spite of the fundamental difference in posture, surprising similarities in occurrence and organization of structures exist in the two types of bodies. CHARACTERISTICS OF THE MAMMALS IN GENERAL The Class Mammalia constitutes the "highest" of the classes of the Vertebrata. The term "highest" implies more specialized perfection of structure and function in meeting environmental influences. This indicates that the class exhibits a large number of characters and considerable complexity. However, greater complexity is not found in all structures. For instance, the mammalian skull compared with the skull of the bony fish is relatively simple, through a reduction in the number of bones making it up. In the mammal, the lower jaw is composed only of two bones fused in the mid-line. Yet, as a biting structure, it is more e1e.cient than the jaw of a fish which is composed of several bones. However, the increased effi-

21 GENERAL CONSIDERATIONS 15 ciency of the mammalian skull is due chiefly to a more precise and effective articulation, rather than to the reduction of bony members. We should recall here that the mammals possess the basic characteristics common to all Vertebrata, but they exhibit certain additional and distinctive characters that place them in a special class. These special characters of the class are described below. 1. The presenct) of mammary glands is diagnostic and is the characteristic from which the class derives its name. All types of mammals possess mammary-gland tissue which actively secretes milk. 'fhese structures, although typically present in both sexes, are entirely rudimentary in the male. Mammary glands are derived from the skin and are usually re': moved in skinning. Since the young of mammals are nourished from these glands, they are thereby forced W associate with the mother for a considerable period. This may be significant in the advancement of the group. 2. Hair is present, which is also a derivative of the skin. In some species of truly aquatic mammals, it is limited in distribution to a few bristles on the lip. Hair follicles usually assume a dilstinct pattern in each species. The term "hair" should not be confused with similar appearing structures such as cilia or chitinous material found among other animal groups. Hair is as characteristic of the mammals as are f(lathers of the bird. The functional importance of hair or fur lies in helping maintain temperature and in protection. 3. A muscular and tendinous diaphragm is always present. This forms a complete partition across the body cavity (celom), dividing it into a superior thoracic cavity and an inferior abdominal cavity. The diaphragm is of great functional importance in perfecting the respiratory mechanism. It is also of importance in parturition, the process of giving birth. This. structure in the mammal should not be confused with the so-called "false diaphragm" of the sharks since the latter serves only to separate the heart cavity from the rest of the body cavity. 4. A single aorta from the heart occurs which bends sharply to the left in an arch. Since the aortic arches arise as paired structures, it is evident that only the left of the systemic pair persists in mammals. The circumstance that the left arch is present makes this character distinguishing. In the birds there is also a single aortic arch, but it is the right arch that persists. 5. The lower jaw bone, or mandible, consists of a single bilateral pair of bones, the dentaries, which become firmly fused in front. The dentaries articulate behind with the squamosal portion of the temporal bone. Thus, we may further say that the temporals bear an articular surface for the mandible. These are diagnostic characters of the mammals. 6. Seven cervical, or neck, vertebrae are characteristically present. The skull articulate~ upon the first of these (the atlas) by means of a pair of rounded processes (condyles) of the occipital bone. In whales and dolphins, the cervical vertebrae may be fused together to act as a stem

22 I' 16 FUNCTIONAL ANATOMY OF THE MAMMAL for the skull. In sloths, there may be as few as six cervicals in some species or as many as nine in others. All variations from seven, however, occur in the more obscure groups of mammals. 7. The ribs (except in the whales and some of the lower mammals) possess two articular processes at the articulating point with the vertebral column. The location of the rib tends to be between vertebrae (intervertebral) rather than in direct line with the rib vertebr~e. Thus, each of the two heads articulate with a separate vertebra. This characteristic may be stated at:': "vertebral articulation of ribs is by means of two processes, an anterior capitulum and a posterior tuberculum." Some of the ribs, however, in any particular animal may not possess two heads, and a single rib could not be used conclusively in identification unless these characters were present. This conditiop. infers greater efficiency in the use of the ribs as levers of respiration. 8. The middle ear contains a complex of three highly specialized bones: the stapes, malleus, and incus. These small bones have helped perfect the more efficient hearing apparatus of the mammal. The stapes is be-' lieved to be homologous to the columella of lower vertebrates; the malleus is considered as homologous with the articulare bone, which bears the articular surface of the lower jaw of reptiles; and it is believed that the incus is a modified remnant that is homologous to the quadrate or upper articular jaw bone of the reptiles. Observations on the systematic reduction of the bones from the lower forms to mammals and studies of embryonic development support these beliefs. 9. A scapula, or shoulder blade, is present which characteristically bears an anterior process, the coracoid. In other vertebrates (and in the. lowest mammals), the coracoid is present as a separate bone. In the mammal, the coracoid is indistinguishably fused with the scapula. 10. The two cerebral hemispheres of the brain are connected by a distinctive band of nerve fibers, the corpus callosum. The corpus callosum varies proportionally in mammals "lith the degree of brain development of the different groupl? It is very rudimentary in the most primitive mammals, small in opossums and other marsupials, and reaches its most conspicuous development in the primates. It is of functional significance. in nervous coordination between the two hemispheres of the brain. Many other distinctive characteristics occur in the mammals, a few of which deserve mention in passing. The mature red blood cells are denucleated; the skin possesses sweat and oil glands; a larynx, or voice box, is formed at the upper end of the windpipe, or trachea, a movable epiglottis reflexly covers the glottis. With but few exceptions, two sets of teeth occur, which are differentiated into types (heterodont). The openings of the intestine and genital systems are separate (a few exceptions), and the young before birth are nourished through a placenta (two orders excepted). The large number of structural characters consiste';;tly present in such a divergent group as the mammals seems remarkable., In size, the mam-

23 GENERAL CONSIDERATIONS 17 mals range from a tiny field mouse no more than an inch long to the whale of 50 feet or over. Thus, the largest of the mammals may be 600 times longer than the smallest and millions of times heavier (600 3 = 216,000,000), yet retain striking similarity in fundamental parts. Divergence is also extreme in the habitats of the various orders and in the modes of locomotion from absolute swimming to terrestrial and aerial. Only the insects excel or parallel the mammals in these respects. As is generally known, sexual differences, or dimorphism, are common to mammals. The primary sex characters are evident -in the presence of reproductive organs which give rise to the sex cells. The secondary characters are those associated with the character of the primary. The type of secondary characters is dependent upon the germinal gland, i.e., the ovary or testis. Hormones formed by these organs determine structural variations between the two sexes. Except in the young of some mammals, particularly rodents, sex can be easily determined by the external genitalia. In man, the more prominent of the secondary characters are found in, the distribution and character of the hair, the relative size of the larynx, and the conformation of the pelvis, together with its breadth in relation to that of the shoulders. The development of the mammary glands of the female at puberty belongs also to this group of characters. In most mammals, a conspicuous difference occurs in size, the male being usually larger and more muscular. Principal orders of mammals (present-day groups) The following is a brief classification of the principal orders arranged on the basis of the degree and number of structural specializations exhibited by typical representatives of the groups. For detailed explanations and further characteristics, the student is referred to Osborn, "The Age of Mammals"; Gregory, "Orders of }\Ifammals" and "Studies on the Evolution of Primates"; and Beddard in the volume on "Mammalia" of the Cambridge Natural History series. The arrangement followed here is mostly from Romer's publications. 1. Monotremata. The monotremes are the egg-laying mammals, consisting of a few species native only to Australia and near-by islands. The typical representatives are the Australian anteater, Echidna (spiny), and the duckbill, Ornithorhynchus (bird-like nose). The more striking characters are as follows: the pectoral girdle has separate coracoid, precoracoid, and interclavicular elements; no teats are present, the nourishing fluid being secreted through simple ventrolateral openings; the young are hatched from the eggs while outside the body and are presumed to lap up the milk as it 'is secreted. The genital tract and alimentary canal open together into a shallow common passage, the cloaca; the oviducts open separately. The older is so distinct from others that it is given also a subclass rating, Prototheria, meaning first animal.

24 18 FUNCTIONAL ANATOMY OF THE MAMMAL 2. Marsupialia. Marsupials are those carrying the larva-like young in an abdominal pouch that encloses a series of nipples and is supported by a pair of epipubic bones; the vagina is double; the brain is primitive and smooth. The common examples are the opossums and kangaroos. Most representatives of marsupial mammals are native to Australia, and these are rather numerous in species superficially resembling moles, cats, anteaters, rabbits, wolves, etc. Huxley considered the grqup as being different enough from other orders to warrant a subclass distinction, which he called Metathcl'ia. In neither the monotremes nor the marsupials are the developing young characteristically nourished by means of a placenta similar to that of the higher forms. Most marsupials develop embryonically in a sort of "uterine milk." The opossum, Didelphys virginiana, is the only species of the order native to North America. Some authorities believe that the marsupials should be considered within the same subclass as higher mammals, the Eutheria, or later mammals. It is evident that marsupials are not so distinctive a group as the monotremes. 3. Insectivora. This is the lowest order of the so-called "clawed" mammals. They are very primitive animals and mostly small. The order includes the moles, hedgehogs, and shrew. The shrew is a small animal superficially resembling the rat. The snout is generally long; the teeth are primitive, generally 44 in number and more or less generalized; the auditory region of the skull is poorly ossified; the brain is small and smooth; the feet are plantigrade. 4. Chiroptera. The bats are markedly specialized only in that the digits of the forelimbs are elongated and supplied with thin folds of skin enabling them to fly. Otherwise the bat resembles the insectivores in many respects. 5. Dermaptera. According to some authorities, this rather obscure group represents an intermediate position between insectivores and true bats. The flying lemur is the best known of the group. A fold of skin is formed between the appendages which is used as a glider, somewhat as in flying squirrels. The fingers are not elongated as in true bats. 6. Primates. These mammals have five digits on both the fore and hind limb; the forelimb is adapted for grasping, and the heel is applied to the ground in locomotion, or is plantigrade in position. A well-developed clavicle is present. The orbital space of the skull is separate from the temporal depression and faces predominately forward rather than laterad. Teats are usually axillary or thoracic in position. A cecum, or blind pouch of the large intestine, is always present and mayor may not continue as a vermiform appendix. Some of these characters are not entirely diagnostic but together are sufficient to characterize the order that include~ the lemurs, monkeys, apes, and man. 7. Carnivora (Flesh-eating animals). The mamfi\als of this order have sharp cutting teeth; the canines are large and usually curved. The incisors are small, from four to six in number. The digits are never less than four, usually with sharp strong claws. The clavicles are incomplete

25 GENERAL CONSIDERATIONS 19 or absent. There are two suborders: one aquatic, including the walrus, sea lion, and seal; and the other terrestrial, including the dog, bear, raccoon, lion, cat, etc. The second suborder may be further defined as having nearly always six poorly developed incisors and limbs that are not modified as swimming appendages and that are usually digitigrade. 8. Ungulata. This is an extremely large group of highly specialized terrestrial mammals. Two divisions are commonly giv'en: the odd-digitated (Perissodactyla)' and the even-digitated (Artiodactyla) forms. These may also be considered as separate orders. In the first ~roup is the zebra, tapir, African rhinoceros, horse, etc.; in the even-digitated group are such common species as goats, sheep, cattle, deer, and swine. The latter group includes forms known as "cud chewers," or ruminants: cattle, giraffes, goats, camels, etc. They characteristically swallow their coarse food rapidly and later bring it back up for further mastication. This process involves a highly specialized stomach. 9. Proboscidea. The elephant has many similarities with the ungulate division and in many ways is one of the most highly specialized forms. The elongated nose and lips, particularly the upper; the extreme size; the tusks and the arrangement of the leg bones are striking features. 10. Cetacea. Whales, dolphins, and porpoises comprise this group. Many profound specializations occur in this order, although several features ~ be considered of a degenerate character. This is seen in the loss of.ir and claws and in the extreme modifications of the limbs when present. An unusually thick layer of fat occurs under the skin to serve as insulation; the forelimb has developed aceessory digits in addition to the usual five; the stomach is extremely specialized; no external neck is present; the skull is built like a wedging block, and the neck vertebrae serve as a rigid stem for this block. Some representatives are extremely large. Because of the great specialization, the group occupies a high phylogenetic position, even though high brain development is not one of its pj.:incipal characters. 11. Rodentia. The rodents are mostly small and numerous as to species. This order includes the rats, mice, squirrels, rabbits, prairie dogs, beavers, guinea pigs, and many others. The incisor teeth are extremely well developed and assume a chisel-like form. No canines are present. Their intelligence is usually low. Rodents are omnivorous as to diet. Usually the testes do not descend into a scrotal sac. 12. Xenarthra. This is a rather diverse group previously known as Edentata, which was not a good term since some representatives bear some teeth that appear degenerately specialized. The group includes the sloths, armadillos, and ant bears. They are highly specialized in some respects but may have reached a more advanced racial development at an earlier period than is now evident, and most of the extreme specializations do not appear to lead to a successful advancement. For our purposes, the above incomplete classification will suffice to illustrate the various types of existing mammals. It should serve to show the

26 20 FUNCTIONAL ANATOMY OF THE MAMMAL general position of man in relation to other mammalian forms. From this review of the orders of mammals, and by supplemental reading, the student should grasp the significant point of adaptive specialization in animals in relation to their functional activities. Further classification of cat and man According to the present arrangement of the orders, the carnivores are regarded as the next higher above the primates. This m~rely means that the typical repref-entatives of the order to which cats belong are considered to possess more or greater specializations than do the representatives of the primates. Here it should be noted that taxonomy, or orderly classification of animals, rests principally upon morphologic features. Such features as intelligence and relative size or quality of the brain are not of so great taxonomic value as are differences in the number of digits or types and numbers of teeth. CAT Family Felidae. Carnivores with five digits in the front limb and four in the hind limb. There are six incisor teeth, two canines, two or four premolars, and two molars in both the upper and lower jaw. There is a bulb or bulla enclosing the ear bones from below. Cats, lions, leopards, etc. Genus Felis. The claws are more completely retractile and typically sheathed. Legs are relatively shorter than those of other genera. The molar is usually suppressed and not in line,vith other teeth. Coloration is varied, as spots in the leopards, stripes in the tiger, the more solid coloration of lions, and the mottled appearance of the jaguar. Most cats are rather closely related structurally. The differences most obvious are in size and coloration, although some differences occur in the skull bones of various species. Species F. domestica. The common house or alley cat is thought MAN I Family Hominidae. Primates collectively known as modern and fossil man belong to this family. They are distinguished from other primates (Simiidae, the anthropoid apes) more by the degree of the development of the characters present. The anatomical points of difference are due chiefly to the more erect position. The brain case is relatively large, the incisors are better developed with the canine usually suppressed; and there is no gap (diastema) between canine and incisors. In both ape and man the same number of types of teeth occur, however. Most apes use the forelimbs to some extent in walking, whereas in man they swing freely. In man the tendency is toward less hair, more ineffective teeth, a rather rudimentary little toe, emphasis of brain, etc. Genus Homo. The modern a~d prehistoric type::! of man are ordinarily placed in this single genus, although most authorities consider

27 GENERAL CONSIDERATIONS 21 to have descended from a wild cat of Asia which, after domestication and introduction into England several centuries ago, possibly interbred with wild cats native to that country. Man has undoubtedly had much to do with the present character of cats and by making selective crosses has produced the several varieties. The varieties of cats, however, are neither so numerous nor so distinct as are those of the domestic dogs. certain prehistoric forms in other genera, as, for example, the Java ape man (Pithecanthropus ereetus). Species H. sapiens. All modern and some prehistoric forms of man are included in this species by most authorities. The characters that distinguish the races are proportionate differences in structures common to all races rather than in the possession of new or different structures. The characters include skin color, hair form, facial features, stature, and ratios of proportions of body regions. When intercrossed, all races of man are able to produce fertile offspring. This is a test for determining species. ANOMALOUS AND VESTIGIAL STRUCTURES Structures of individuals within a species frequently differ greatly from the usual or average condition for the species. An extreme variation that occurs rarely is known as an "anomaly." Before establishing a structure or condition as anomalous, it is necessary to check on several individuals to determine whether the variation is common or unusual to the species. Extreme variations may occur in any of the systems. Often there is no apparent effect upon the animal possessing anomalous conditions, and many humans possess anomalies of which they are unaware. The mammals are particularly susceptible to anomalies because they must pass through so many embryonic changes in reaching the adult condition. These changes are partly correlated with the phylogenetic evolution of man or racial history, and there is an occasional tendency to reestablish some of the so-called "ancestral characteristics." An extra pair of ribs in man or several additional tail vertebrae are not especially rare anomalies. Supernumerary or additional nipples occur as anomalies in man, indicating an earlier linear distribution of mammary glands. Occasionally, certain muscles may be entirely absent or remain as mere vestiges as compared w-ith the average. Another circumstance commonly met is the misplacement of the visceral elements with respect to the surface landmarks or associated structures. Perhaps the most common anomalies are present in the vascular system. These will be discussed in connection with that system. The vestigial structures are remnants of structures that appear to have once had functional importance. A classical example of a vestigial struc-

28 22 FUNCTIONAL ANATOMY OF THE MAMMAL ture in man is the vermiform appendix of the large intestine. In some mammals, especially rodents, an extension of a similar character is structurally and functionally prominent. In man, the appendix apparently represents a degenerate remnant of an important part of the digestive tract of our ancestors. Fortunately, few of our remnants of the past cause so much trouble. Ear SC(crococcygeal Tail ligame17ts 0 FIG Vestigial structures in man. A, muscles of the ear, msplayed by removal of the superficial tissues. B, appendix, seen from behind. C, embryo, showing the tail. D, abnormal persistence of tail muscles in adult, seen from behind. (A compiled from works on human anaj.omy; B, C, and D from Romanes, " Darwin and after Darwin," Part 1, The Open Court Publishing Company. From Wolcott "Animal Biology.") Man still retains vestigial muscles that are thought to once have ml1de ear movements possible in ancestral forms. Only a few gifted individual;:; now have any conscious control of these muscles. The tail vertebrae of man degenerate and become fused into a single element called the coccyx. Evidences from embryology and comparative anatomy indicate it to be a vestige. Many other structures appe'ar to belong in this category. Frequently, it is difficult to determine whether a part is degenerate or merely in a primitive beginning stage. The term "rudimentary" has unfortunately been applied to both conditions. For example, the little toe of adult mali apparently is not so well developed, compared with the other toes, as it is in a baby. It is sometimes said to be rudimentary. Compare.d with other anthropoids, the little toe of man is degenerate and apparently destined to become a vestigial toe. Functional considerations should always be correlated with morphological determinations of this character. -

29 Chapter II THE SKELETAL SYSTEM A STUDY of a prepared skeleton, even with the bones fastened together (articulated) in their proper positions, is little more than suggestive of its true functional character in the living body. Obviously such a skeleton, dried and cleaned, represents only the nonliving elements, or intercellular materials, that persist in the process of preparing bones for study. Bones, therefore, make up a sort of framework of the true skeleton of the body as it exists functionally. Despite these circumstances, an articulated skeleton introduces, as well as any other system, the complexities of the organism and the interdependence of the various systems in the economy of the body as a whole. Most of the details of the skeleton have little or no significance of themselves and are best studied in connection with the muscular system, with which the skeleton functions most closely, and with the nerve outlets of the skull. Muscle dissection should be done concurrently with a detailed examination of skeletal parts. In the living body, the bony skeleton is intimately associated with other skeletal tissues such as cartilages and ligaments. Each bone is covered with a tough membranous sheath, the periosteum, except for surfaces that move on other bones. The periosteum contains both bone-building cells, osteoblasts, and bone-destroying cells, osteoclasts. During growth, both types of cells are normally active. When a bone is injured, the sheath is also damaged and the irritation stimulates the bone-forming cells to great activity. Consequently, the periosteal sheath is necessary in bone repair. Cartilages that are functionally associated with the bony skeleton are of several kinds. The vertebrae are separated by disks of fibrocartilage; the cartilaginous extension of the nasal septum is a translucent gristle; the ends of the long bones are covered by a smooth glassy-appearing articular cartilage. The bones are held together at movable joints by special bands of ligaments and membranous enclosures, which may be observed following the dissection of muscles. FUNCTIONS AND DIVISIONS When viewed as.a whole, the skeletal system performs three distinctive functions: (1) it for~s the internal foundational material and framework for the direct and indirect support of all other tisslfes; (2) by means of 23,

30 24 FUNCTIONAL ANATOMY OF THE MAMMAL M. :;; muscle M. TrapeziuS" {\- I \ I \. I I -Mandible I \ I \~ M. Trice.ps... M. Pectora lis... Sternum, 11th Rib, '... '-M. txt. oblique M. Sartorius -<:Pubis -- -,_..., 'Femur ---M. T. fascia (ata - --_ Patella ---- M. Biceps femoris ---- Tibia --- fibula M.Gastrocnem;us, -: Torsals ' :. _'Metatarsals, FIG Skeleton of the cat in relation to superficial muscles. In the later dissection of the muscles, the underlying skeletal parts should be visualized. (Drawn by John F. Trainor. ) joints between rigid parts, the skeleton serves a leverage function, allowing for motion and locomotion through the contraction of attached muscles; and (3) the bony elements are arranged to provide protection for the more vital and sensitive organs. The protective function is illustrated particularly by the arrangement of the thoracic basket protecting the heart and lungs and by the cranial bones and vertebral column housing the central nervous system.

31 THE SKELETAL SYSTEM 25 The skeleton is ordinarily divided, for purposes of study, into (1) the axial portion consisting of the skull, vertebral column, ribs, and sternum; and (2) the appendicular division, made up of the elements of the thoracic and pelvic girdles together with the series of limb bones extending distally from them. One should especially note that the girdles supporting the limbs operate at right angles to the axial portion of the skeleton and are, therefore, par,ts of the appendicular complex of bones. FIG Skeleton of the domestic cat. divisions of the skeleton. Note particularly the structural and functional (From Storer, "General ZooloIJY.") The skeleton of adult man is usually described as consisting of 206 separate bones. Many bones that are formed from a number of centers and that retain conspicuous divisions in early childhood are considered as "separate bones." Examples of such bones are the sternum, sacrum, hip bone, and certain skull bones. Of the 206 bones, 172 are paired (86 pairs): 11 pairs in the skull (including ear bones), 12 pairs of ribs, 31 pairs in the thoracic appendages, and 32 pairs in the pelvic appendage including the patellae, or kneecaps. Unpaired bones are median in position, although some are formed by a rather late fusion of bilateral halves. These comprise 6 in the skull, 1 hyoid, 1 sternum, and 26 vertebrae. Several more bones occur in the cat than in man, but none are of a new type. The cat possesses 7 instead of 5 lumbar vertebrae and a variable number of tail vertebrae represented by a single coccyx in man. The cat also possesses 13 pairs of ribs instead of 12, and the early elements of the sternum never fuse into one separate element but remain as segmental sternebrae. Except-in extremely old cats, different elements of separate skull bones are usually more pronounced than their homologues in man.

32 26 FUNCTIONAL ANATOMY OF THE MAMMAL Fewer bones occur in the hind limb of the cat, because only four digits occur in the hind limb. FIG Skeleton of man. (From Millard and Kin(J, "Human Anatomy and Physiology.") ORIGIN AND TYPES OF BONE Bone originates in fetal life by the laying down of mineral substances ' in a tissue of a softer character. The process of bone->formation is known as ossification, and the points at which ossification begins are known as ossification centers. A long bone, such as the humerus of the upper arm,

33 THE SKELETAL SYSTEM 27 is formed from three such centers, one at each end, the epiphyses, and one in the middle, the diaphysis. The diaphysis is established relatively early in development, but even at birth the heads of the long bones are not well ossified, and in man they do not firmly join the body (diaphysis) of the bone for several years. The separate elements of the skull arise from separate centers of ossification. At birth, certain of these bones also have, FIG A longitudinal section of the head of the femur. Note the structure of compact and spongy bone. The periosteum is shown cut and partly pulled aside. (From Rogers, Hubbel. Byers, "Man and the Biological World." Redrawn from Williams, " Textbook oj Anatomy and Physiology." ) not yet joined, thus leaving soft areas between known as fontanels. Later in life, some of the elements that arise separately may fuse so completely as to be indistinguishable from each other. A series of fetal animals stained and cleared to show bone formation is invaluable in a study of the separate elements of the skeleton and their relationships (see Appendix). Bone arises developmentally in three different types of earlier tissue: (1) in cartilage, (2) fn a membrane-like sheath of dermal tissue, and (3) in tendons. Bone arising in a development of preformed cartilage is known as replacement bone, and most of the bones of the body are formed in this

34 28 FUNCTIONAL ANATOMY OF THE MAMMAL ) way. The skull possesses both replacing boiie and bone formed in a dermal membrane. The floor, side walls, front, and back of the brain case are preformed in cartilage; whereas, the roof joins these parts first as a membranous sheath, later ossifying as dermal, or investing, bones. Early cartilaginous bars representing the jaws also become invested by dermal tissue which ossifies into dermal bone. Bones formed in tendons are known as sesamoids. The kneecap (patella) is the most conspicuous example of sesamoid bone, but sesamoids also occur in the wrist. Occasionally, extra sesamoids "'11 develop in the tendons as a result of injury or from constant irritation and may become very troublesome. FIG. 2.S.-A diagram to indicate the character of bones and muscles as organs and the mode of attachment of a muscle to a bone. (From Wolcott, "Animal Biology.") Terms used in describing bones angle-corner of a bone, found between two borders. articulation (ar-tik-u-la'shun)-a joint or union between two bones. border-the edge of a bone; usually applied to flat bones. capitellum (kap-it-el'um)-a small head. capitulum (kap-it'u-lum)-literally means same as above but is applied differently. caput (ka'put)-"head," a rounded enlargement at the end of a long bone. condyle (kon'dil)-a smooth rounded articular surface; in pairs. corpus (kor'pus)-:-"body," the largest or principal part of a bone. crest-an eminence; usually a ridge with a sharp edge. diaphysis (di-af'is-is)-central portion of a long bone; ossification center. epiphysis (ep-if'is-is)--enlarged end of a long bone.. facet (fas'et)-small articulation face; smooth limited area. fissure-a narrow cleft in a bone.

35 THE SKELETAL SYSTEM 29 fontanel (fon-tan-el')-unossified (at birth) region between skull bones. foramen (for-a'men)-literally a "window" or opening through aobone. foramina-plural of foramen. fossa (fos'ah)-a concavity or depression; literally a "ditch." groove-an elongated concavity between parallel ridges. lamina (lam'in-ah)-a sheet of bone; a flattened portion. linea (lin'e-ah)-.--literallya "line"; narrow crest or ridge. malleolus (mal-e'o-lus)-a hammer-headed protuberance. manubrium (man-u'bre-um)-a flat handle-like projeclion. neck-a constricted portion immediately below the "head." notch-a deep or large indentation (usually for articulation). pedicle (ped'ik-el)-a column or base supporting an arch. process-an extension or projection of a bone. ridge-a narrow roughened elevation on the surface. shaft-that part of a long bone formed from the diaphysis. sinus-a pocket or cavity; applied principally to cavities within the skull. spine-a more or less sharp projection or short ridge. squama (skwa'mah)-theo flat portions of the cranial bones. styloid (sti'loid)-literally "pencil shaped"; a pointed process. sulcus (sul'kus)-a furrow or groove, intermediate between fissure and fossa. suture (su'tur)-the line or union between two immovable bones. symphysis (sim'fis-is)-a union in which two bones are firmly connected by cartilage. trochlea (trok'le-ah)-an articular surface having a pulley shape. tubercle (tu'ber-kl)-a small rough eminence; usually for muscle attachment. tuberosity (tu-ber-os'it-e)-a large uneven tubercle or eminence. General features of the mammalian skull The skull presents many more complexities than other parts of the skeleton, and this preliminary discussion may be helpful. In general architecture, the skull is roughly analogous to a three-story house and thus exhibits three functional levels. (1) The upper floor (neural level) supports and protects the brain; (2) the middle floor serves as a passageway for respiration; (3) and the first floor (alimentary) serves in the intake and mastication of food. In this analogy, the roof of the mouth is the floor of the respiratory passageway, and the floor of the brain case acts also as the roof of the respiratory channel together with the nasal bones, which extend in front of the cranium. The bones that enclose and support the brain make up the cranium, or brain case. The cranium also supports and 'protects the organs of special sense: optic, olfactory, and auditory. Bones of the skull that are not concerned with the neural function are the facial bones, located roughly from

36 30 FUNCTIONAL ANATOMY OF THE MAMMAL the level of the bridge of the nose to the lower jaw. In man, the face is relatively suppressed, and the neural level is greatly emphasized and dome-shaped (Fig. 2.7). It is interesting to follow the shift of emphasis and comparative development of the levels of the skull from the lower mammals such as opossums to the monkeys, higher apes, and man. The skull of a lion with open jaws strikingly illustrates the extreme difference between the carnivores and man as to the proportionate importance of visceral and neural functions in the two forms. C R A N 1 U M F A C E FIG Fullctional levels in the skull of the cat. C R A N I U M F A C E FIG Functional levels in the skull of man. Compare with Fig In all mammals, the different bones of the skull occupy the same positional relationships with each other and are remarkably constant in their occurrence. For this reason, it is advantageous to figure these relationships in a generalized scheme or map. The skull of most primates (including man) is more compact than that of other mammals, and the exits of the cranial nerves do not occur in such a distinct serial pattern as in an elongate skull. For detailed examination of separate elements, the skull of a young animal is preferable since many of the sutures between bones tend to become indistinct in older specimens. Some of the features must be seen in a sagittal section or in a disarticulated skull.

37 THE SKELETAL SYSTEM 31 J Hyo id ~ apparatus { a l.orynseal cartilo,!es 00 I to XII Cranial nerve exits FlG Typical arrangement of bones in the Inammalian skull. Cartilaginous bones a r e stippled. The hyoid is also of cartilaginous origin. FIG Diagram of the skull of the newborn child. Cartilaginous bones are stippled ; membrane bones unsha<ied; derivatives of the vi~cera l arches are shaded vertically; fontanels are shaded diagona1'!y. a, alisphenold ; t, frontal; h, hyoid; m, mandible; m.e., Meckels cartilage; mx, maxilla; 0, occipital; p, periotic; pa, parietal; sq, squamosa!; st, styloid process; t, thyroid cartilage; ty, tympanic; z, zygomatic Or malar. (From Weiman, "Vertebrate Embryology.")

38 32 FUNCTIONAL ANATOMY OF THE MAMMAL SKELETON OF THE CAT Axial division The skull. The following description of the cat skull is given with the assumption that the student will have the actual material before him; reference should also be made to figures. Conspicuous landmarks should first be noted. Observe the sagittal suture occupying the middorsal line from the cranial to the caudal end of the skull. Note the position of the orbital fossae (eye sockets) which in the cat are continuous with depressions just caudad to them, the temporal fossae. In man the orbital fossa is separated from the temporal depression by a complete rim of bone at the back of the orbit. The cheek bone, or zygomatic arch, forms the lower rim of the orbital fossa and extends back over the temporal depression almost to the ear opening, the external auditory meatus. Observe that between the floor of the brain case and the hard palate are the paired respiratory passageways, which begin in front as paired external nares. The floor of the brain case ends caudally at the large opening, foramen magnum, which arbitrarily marks the position of the junction of the brain and spinal cord. On either side of the foramen magnum smooth rounded projections occur, the occipital condyles, which articulate with the first cervical vertebra, the atlas. Brain case. The brain case should be regarded as a box-like structure possessing a floor, side walls, roof, front, and back. A modified ring of bone surrounds the foramen magnum at the back, or base, of the skull. This is the occiput, made up of a dorsal supraoccipital, a ventral basioccipital, and the paired exoccipitals which bear the occipital condyles. The basioccipital fuses cranially with the basisphenoid, which is characterized by possessing the deep pituitary fossa seen from within or in sagittal section. Craniad to the basisphenoid is the more narrow presphenoid which encloses the sphenoidal sinuses also seen in sagittal section. These thre~ median bones form the floor of the brain case; bones further anterior belong to the face. Beginning at the back of the skull again, the side wall in front of the exoccipitals consists of the temporal complex of bones and lateral sphenoids. All the bone surrounding the ear opening is temporal. The flat portion above the opening and which bears the zygomatic process of the cheek arch is squamosal. Directly back of the ear opening is a mastoid process, which in man is very prominent and possesses honeycomb-like cavities (mastoidal cells or sinuses). Beneath the ear opening is the bulb-like tympanic bulla,

39 THE SKELETAL SYSTEM 33 which in man is represented by the pencil-like or styloid process. A small opening occurs between the undersurface of the mastoid process and tympanic bulla, the stylomastoid foramen through which passes a branch of the facial nerve. Occasionally this nerve is injured in mastoid operations in man, resultipg in paralysis of facial muscles of expression. The lateral sphenoids consist of two parts that are indistinguishable in old specimens and that also become fused 'iith the median Incisor Foramina I. Incisive 2. Infra-orbital 3. Palatine 4. Mental s.lacrimol canal 6. optic!. sph enoida I fissure B.Rotund~m ~n,: t-nr' h i ta I process 9. Ova Ie of juqal Zyqomatic process uamosal lo.eustachian tube and Facial II.Jugular Il.stylomastoid "Postorbital process of frontal B _ Alisphenoid Basisphenoid panic bulla asiocci pita I Exoccipital [>coccipitaf condyle '~ ndibularfossa Anqular process FIG. _ Dorsal, ventral, and lateral views of the cat skull. Dentary D (Modifi ed from Mi~(1rt.)

40 3.t FUNCTIONAL ANATOMY OF THE MAMMAL sphenoids of the floor. These are the ali- and orbitosphenoids. They are best described with reference to the exits of the cranial nerves (foramina). Looking directly into the orbital fossa, four openings are seen in a continuous row. The first of these is the optic foramen through which passes the optic nerve. It is surrounded by orbitosphenoid bone. The next opening is the largest of the series and occupies a position between the' ali- and orbitosphenoids. Th~s is the sphenoidal fissure (foramen lacerum). The other two foramina are the rotundum and ovale, both surrounded by the alisphenoid which extends dorsally in a wing-like expansion, the wing of the sphenoid in man. The foramina of the skull will be further described later in a tabulated form. The roof of the skull, from back to front, consists of the supraoccipital, paired parietals (an interparietal also in the cat), and the more posterior portions of the frontals. The brain does not extend craniad as far as the nasals so that the frontals cover a part of the brain and also contribute to the roof of the nasal passageway. The true front of the brain case is closed off by a vertical transverse partition of ethmoid bone which separates the case from the nasal cavity. This partition may be seen by looking into the foramen magnum with proper light. In the extreme cranial end of the case will be seen paired depressions housing the olfactory lobes of the brain. The forward enclosure of these lobes is the partition referred to and is known as the cribriform plate of the ethmoid. It is characterized by numerous olfactory foramina through which olfactory nerves reach the olfactory lobes of the brain from the sensory epithelium of the nasal cavity. Facial bones. The most prominent of the facial bones are those of the upper and lower jaws. The part of the upper jaw bearing the incisor teeth is premaxillary. Other teeth of the upper jaw are imbedded in the maxillary bone. The lower jaw consists of the paired dentaries making up the entire mandible. The dentaries articulate by means of mandibular condyles which fit into mandibular fossae on the undersurface of the zygomatic process of the squamosal. In addition to the premaxillary and maxillary, the roof of the mouth contains the palatine bone, which lies caudad and mediad to them. Back of the hard palate are vertical extensions of the palatine bone which support the soft palate and above which air passes to the larynx. These extensions terminate in a pterygoid bone as the hamular process and together with the floor of the brain case form an inverted trough. The pterygoids are closely' associated also with the lateral sphenoids.

41 THE SKELETAL SYSTEM 35 Immediately above the nasal openings are the nasal bones, which join with the frontals further back. An extension from the maxillary bone forms the lower rim of the orbital fossa. This is the malar bone, sometimes called the jugal bone in lower vertebrates. Just within the orbital fossa near the front is the lacrimal bone, which may be recognized by the lacrimal canal that penetrates it and carries the tear duct to the nasal cavity. Postorbital processes of the frontal and of the malar bones form the back.rim of the orbital fossa. These do not join except in the primates. In this order (including man) the caudal rim of the orbital fossa is complete, thus separating the' fossa from the temporal depression that lies back of the orbit. At the junction of the maxillary and malar toward the front and lower rim of the orbit is the prominent opening, the infraorbital foramen. Other features of the skull are shown in the figures and following tables. The foramina of the skull These foramina may be classed as (1) primary exits for,the cranial nerves as they leave the brain case and (2) passageways for structures (principally nerves) through the facial bones. They are tabulated below and on the following page: CRANIAL NERVE EXITS (CAT SKULL) Foramen Bones involved Cranial nerves involved 1. Olfactory.... Cribriform plate of the ethmoid (I) Olfactory from nasal epithelium 2. Optic.... Orbitosphenoid (II) Optic from retina of eye 3. Sphenoidal fissure (orbital fissure) (foramen lacerum anterior) 4. Rotllndum... AliRphenoid 5. Ovale Alisphenoid Alisphenoid and orbitosphenoid (III) Oculomotor, (IV) trochlcar, and (VI) abducens to the extrinsic muscles of the 6. Facial canal Petrous and tympanic bulla 7. Stylomastoid... Tympanic and mastoid 8. Internal acoustic Petrous (inner view) meatus 9. Jugular... Tympanic and basioccipital Hypoglossal canal Exoccipital (inner margin) \. eye; ophthalmic division of (V) trigeminal (V) Maxillary division of trigeminal (V) Mandibular division of trigeminal Branches of (VII) facial nerve (VII) Branch of facial (VIII) Auditory nerve (IX, X, XI) Glossopharyngeal, vagus, and spinal accessory nerves; intcrnal jugular vein (XII) Hypoglossal nerve

42 36 FUNCTIONAL ANATOMY OF THE MAMMAL F AcrAL OR N ONCRANIAL FORAMINA Foramen Bone surrounding Structures passing through 1. Incisive.. '..., Horizontal parts of maxillary Nasal artery and nasopalatine and premaxillary branch tjf trigeminal nerve 2. Infra-orbital..... Maxillary at malar region Infra-orbital branch of maxillary 3. Lacrimal, ".. Lacrimal bone just dorsal to Tear duct or lacrimal canal 4. Sphenopalatine Posterior palatine.. 6. Eustachian Mental (superior may be varied) 8. Inferior dental,.., infra-orbital foramen Vertical palatine just posterior Sphenopalatine nerve to infra-orbital foramen; proceeds to penetrate horizontal palatine Vertical palatine just back of Palatine artery and nerve sphenopajatine Tympanic and basisphenoid Eustachian tube to facial canal Mandible; on lateral surface Branches of dental nerves and beneath and slightly poste- vessels rior to canine tooth Mandible; on medial surface Leads to "dental canal" which anterior to condyle carries the dental nerves and vessels The vertebral column The vertebral column consists of a series of homologous bony segments that are structurally &ifferentiated into five groups: cervical! thoracic, lumbar, sacral, and caudal (coccyx of man). The \ vertebrae of each group are not abruptly different from an adjacent '. group, but a gradual transition of one type to another occurs in keeping with the functional relationships. Thus, the last of the seven neck vertebrae Ccervicals) does not resemble the first cervical as much as it resembles the first thoracic to which it is adjacent. The last, or thirteenth, thoracic bears a close resemblance to its adjacent first lumbar. The lumbars may be considered most genemlized and primitive in their structural character since they are relatively free from any highly specinlized function other than support. From a description of a typical lumbar vertebra, suitable comparisons may be made with the other types. Lumbar. The most conspicuous and constant feature of a vertebra is the neural canal through which passes the spinal cord. The cord terminates in the caudal vertebrae as ad nonnervous filum terminale. The neural canal lies above the body of the vertebra,

43 THE SKELETAL SYSTEM 37 or centrum, from which side walls project dorsally. The b ases of the side walls are pedic1es which support the arch formed by neural lamina. A spinous process, or neural spine, forins the most dorsal part of the vertebra. Transverse processes project from the sides of the centrum, and a small accessory process also extends from the pedicle at its caudal aspect.. Place two lumbar vertebrae together in their normal positions. The facets, or articular surfaces, for the adjacent vertebrae serve in distinguishing cranial from caudal aspects on an isolated vertebra. Vertebral Neural for~aen lamina ". Trans... - process Ant. articular facet ATLAS Art sur. \ tuber:ofr.ib Spinous process Ant. art. facet THORACIC Art. surface co p. of rib Post. articular facet odontoid ~rocess process c..-. "'''' Spinous process ~~it.j/i!.~~ Ma m milia ry process 'Post a rticu 10 facet AXIS 5 th CERVICAL Ant.articular facet pinous process Neural canal Vertebral foramen Centrum LUMBAR Ilium "'.. _ -0 rticu lotion '~1Ift:r Spinous process Tra n s. proc. SACRUM FIG Types of vertebrae-cat. (Modified from kjivart.) Post art. proc. The anterior articulating process (prezygophysis) projects its face (articular facet) dorsally and medially, while the posterior articulating process (postzygophysis) projects its facet ventrally and laterally. This is ~rue of all types of vertebrae and is perhaps the only definite character in properly orientating a single vertebra.

44 38 FUNCTIONAL ANATOMY OF THE MAMMAL An intervertebral notch is formed between two articulate vertebrae for the passage of the spinal nerves. The facing notches of two adjacent vertebrae form the intervertebral foramen for the passage of a spinal nerve. In life, the centra of adjacent vertebrae are separated by a fibrocartilaginous disk, and the vertebrae are closely bound together by means of a complex of ligaments. Cervical. All the cervical vertebrae except the'seventh may be roughly charac~erized by the presence of a vertebral foramen penetrating the transverse process on either side. These foramina carry the vertebral arteries to the head. The seventh has a longer spinous process, and only the upper portion of the transverse process is present. In other features, the seventh closely resembles the first thoracic, which is immediately adjacent posteriorly. The most greatly modified of the cervicals, from a generalized condition, are the first two: the atlas and axis. These are most intimately concerned with the support and movement of the head. Structural differences in the cat and man should be determined in relation to functional planes and gravity influences. The chief features of the atlas is the suppression of the spinous process and the loss of the centrum. The presence of large wing-like transverse processes is also characteristic. The articulating facets for the occipital condyles are large and deeply concave. The axis is adapted to serve as a pivotal center for the atlas. Its characteristic feature is the odontoid process, which is directed anteriorly. This process is described as representing the centrum missing from the atlas which ossifies separately and later fuses with the axis. The spinous process of the axis forms a rather prominent neural crest. Thoracic. The thoracic vertebrae all have a common function in that they serve as articulating points for the vertebral portion of the rib. The transverse processes are highly modified so that they may typically bear small articular surfaces, or facets, for this union. Since a rib tends to be intervertebral in position instead of intravertebral, each rib characteristically joins two vertebrae rather than one. Determine which of the vertebrae possess two facets on each of the transverse processes. All the facets are not easily made out in the cat. The long spinous process is typical of this series and is associated with the deceivingly deep spinal muscles. Compare the functions of the thoracic vertebrae with the cervicals. The. lumbar vertebrae follow the thoracic and have already been described.

45 THE SKELETAL SYSTEM 39 Sacral. The sacral vertebrae are fllsed into what may be considered a single bone, the sacrum. Note the articulation of the sacrum with the pelvis. The number of vertebrae forming the sacrum varies and is determined by counting the spinous processes. The foramina for spinal nerves 're seen on the ventral surface. Determine the functional character of the sacrum as a support to the hip bones, arnd observe its articulation with the ilium of the pelvic girdle. Caudal. Caudal vertebrae of the cat are represented in man by the coccyx, a vestigial series of vertebrae that are of no particular importance. Except in relatively few mammals, the tail is of no functional value. Occasionally, a child is born with several additional coccygeal vertebrae. In the cat, they may vary from the few ill short-tailed varities to as mall;r as 2fi or more ill other rl),ces of cats. They are all very similar in structure but become smaller caudally. Note the absence of the neural canal in these vertebrae. The thoracic skeleton This section of the skeleton is composed of the thoracic vertebrae, already discussed, the ribs, and the sternum. These bones form a complex primarily designed for the respiratory framework and for the protection and support of the more susceptible structures of the thoracic cavity. Although this section is ordinarily considered with the axial skeleton, its dorsoventral projection of the serially arranged ribs involves this axis as prorxlinently as the craniocaudal. The primitive bilaterally flattened forill of the thorax in the cat is reflected in the more rounded chest of!), child at birth, which resembles the shape of the chest of a kitten. Adult cats possess a bilaterally compressed chest; whereas, in man the chest develops dorsoventrally compressed. One may speculate on the advantages of form in the two types. Obviously, a cat can pass through narrow vertical passageways or vegetation to better advantage with the bilaterally compressed thorax. The ribs. In the cat, 13 pairs of ribs are typi'cal. The ribs are directed so that when elevated or pulled craniad an increase in the volume of the thorax results. Inspiration of air is accomplished by elevation of the ribs and flattening the diaphragm. The fifth or sixth rib may be considered as generalized. Its proximal end is slightly thickened into a capitulum which projects dorsa-anteriorly. Posterior to the capitulum is the neck, back of which is a small p~ojection, the tuberculum, articulating with the

46 40 FUNCTIONAL ANATOMY OF THE MAMMAL vertebra immediately posterior to that with which the capitulum Jams. Most of the ribs are therefore intervertebral in position. The curved portion extends obliquely downward, forming an angle and ending in a cartilaginous extension, the costal cartilage, which typically joins the sternum, or breast bone. Hyoid bones Sternebrae Trachea I rin9s LARYNX AND HYOID Tuberculum RIB FIG Axial portions of the cat skeleton. RIBS AND STERN UM (Modified from Mivart.) The nine anterior ribs are considered vertebrosternal ribs because they join the sternum directly by means of their cartilages. The costal cartilages of the next three connect together and with the cartilage. of the ninth (vertebrochondral), while the last forms no ventral connection and is called a vertebral, or floating, rib. In man the last two are of this type. The angle formed by the connecting cartilages is termed the costal angle a,}d is an important landmark in determining the position of the diaphragm.

47 THE SKELETAL SYSTEM 41 It is said that in over 600 human bodies dissected about 5 per cent possessed an additional rib or pair of ribs. This thirteenth rib, usually a cervical, is called a "gorilla" rib since that number is characteristic of gorillas and chimpanzees. For no apparent reason, this anomaly occurs much more frequently in males than in females. Anomalous ribs are not at all uncommon in the cat and are apparently associated 'With the anomalous development of an intercentrum of a vertebra. In the human embryo, as in other mammals, rudimentary ribs are formed on all the vertebrae from the seventh to the coccyx. These normally disappear except for the thoracic. Sternum. This structure in the cat retains its primitive segmental character. A full-term human fetus shows an irregular series of button-like elements of the sternum. The anterior segment is prolonged forward and is known as the manubrium. Then follow six similar segments, the sternebrae, which are much longer than broad. The last segment is constricted and is known as the xiphoid process, which bears an expande~ tip, the xiphoid cartilage. Compare the sternum of the cat with that of man. In man, the xiphoid process is frequently irregular and knobby, indicating rickets. -Hyoid apparatus and larynx. The hyoid consists of a paired chain of small bones and cartilages extending from either side of the thyroid cartilage (Adam's apple) of the larynx in the form of horns which contact the tympanic bullae. In man one can feel this apparatus by pressing firmly with the thumb and forefinger just above the larynx, and by extending the tongue the connection of the extrinsic muscles of the base of the tongue with the hyoid can be demonstrated. The action is best noted in swallowing. The appendicular skeleton The bones of the appendages include the bones making up the girdles of the body, as well as their long free extensions with the attendant distal parts. B~cause of comparative applications, we shall speak oupe anterior, or superior, limb as the thoracic appendage and the posterior, or inferior, limb as the pelvic appendage. In a generalized mammal, considered from the developmental viewpoint, each appendage is furnished with a number and a general arrangement of skeletal parts that are strikingly similar. These similarities were discussed in the first chapter under serial homology. However, the functional arrangement of the bones of the two regions are typically opposite in that the forelimb is a "puller" and the hind limb is a "pusher." This condition apparently arose through rotations in opposite direction of original lateral extensions.

48 42 FUNCTIONAL ANATOMY OF THE MAMMAL The thoracic appendage Thoracic girdle. The girdle consists typically of a scapula with a coracoid process and a clavicle, or collar bone. The clavicle may be entirely missing, as in the horse, or rudimentary, as in the cat. " It is best developed in arboreal forms, such as the opossum and monkeys, and most poorly developed in cursorial, or running, types... ''] j!.'.~ Humerus _ : j./ I.,. L FlO Elements of the thoracic appendage of man and the cat. (By John F. Trainor.) It is typically a key bone (cliethrum) between the sternum and scapula. The student should attempt to account for its appearance from the standpoint of range of action necessary for each type of mammal. The scapula is less 'subject to extreme variations in the different groups of mammals. In the lower forms, the coracoid process is represented as a separate bone, and it develops embryologically in the mammal generally from a distinct ossification center. In origin, the clavicle is unique among appendicular bones in that it is said to be derived from an earlier membrane rather than cartilage.

49 THE SKELETAL SYSTEM. 43 The scapula. This is a greatly flattened triangular bone bearing a conspicuous spine on its lateral aspect and a concavity, the subscapular fossa, on the medial aspect. The proximal head of the humerus articulates in its glenoid fossa, which is surrounded by i;!. rath~r heavy glenoid border. The t>?ln.e Q{ the t>ca?ula terminateb distally in an acromion process. A flattened metacromion process occurs on the sp1ne just above the acromion process. The inferior racoid proc. Vertebra border etacrom ion process Axi lia ry border Infras~ina+us fossa Inferioran'lle FIG Scapula of the cat. (Modified from Mivart.) angle of the scapula is rather acute, while the superior angle is rounded. Between these two angles is the vertebral border. The border from the inferior angle to the glenoid border is axillary; the superior border extends from the superior angle to the glenoid border. The area in front of the spine is the supraspinatus fossa, that back of the spine, the infraspinatus fossa. The humerus. This is the bone of the upper arm, or brachium. Its proximal rounded head articulates in the glenoid fossa, or cavity of the scapula, which was typically a focal point for the three com" ponents of the girdle. Observe the appearance of twisting in the humerus, and determine the direction and degree of rotation. Note the twisting effect on the ultimate position of the forearm. Ridges on the proximal third are named with reference to the insertions of the deltoid and pectoral muscles, to be described later. The larger proximal head is marked by a greater and lesser tuberosity, between which is the intertubercular, or bicipital, groove. Above and on the inner margin ot the distal head is the supracondylar foramen, which is more characteristic of the el.1rly reptilian forms than of

51 THE SKELETAL SYSTEM 45 and each forms a rather complicated articulation with the small carpal; or wrist, bopes. Carpal bones. These extend roughly in two transverse rows and have been variously named in man and other mammals. They are difficult to study in the cat because of their small size and co:rp.plications with variable sesamoids. The row adjacent to the radius and ulna consists of three i_rregulariy shaped bones: the scapholunar, 01ecl"C1non proces~ Coronoid process Radial notch Bicipital tubercle A. Styloid Ulnar surfa B FIG Ulna CA) and radius CB) of the cat. (Modifi ed from Mivart.) the largest and on the radial side; the cuneiform, median in posi-. tion; and the pisiform, a process of which projects prominently on the lateral margin of the wrist. The scapholunar joins the radius above and projects into a depression formed by the arrangement of the second row of four bones. The cuneiform is wedged into position at about the level of the fourth digit and articulates with the ulna. A projecting process of the pisiform is typical. The pisiform is supported almost entirely with the cuneiform above and at the side and the unciform of the second row below. The bones of tl:/_~ second row articulate below with the metacarpals. Next to the unciform on the ulnar side is the os magnum,

52 46 FUNCTIONAL ANATOMY OF THE MAMMAL which is smoothly convex above and roughly outlined below to articulate chiefly with the third metacarpal, although it meets the one on either side also. The trapezoid is rather small and articulates with the second metacarpal only. It is best seen on the dorsal surface of the hand. The most radial of the series is the trapezium, which supports the thumb, or pollex. Its form is that of a saddle with the concavity articulating with the convex surface of the first, or pollex, met3;carpal. Metacarpals. The metacarpals comprise the bones of the hand from the separated digits to the wrist. There is one for each digit, all similar in general form except for the thumb, or pollex metacarpal. The irregularities of the proximal ends fit the carpals, and the more regular distal articulations join the phalangeal bones. A phalangeal formula is derived by counting the number of bones in each digit. The phalanges of the human and cat should be compared. Each phalanx ossifies from a single center at the proximal end. The digits are named from thumb to little finger as follows: pollex, index, medius, annulus, minimus, or simply 1, 2, 3, 4, 5. The action of the thumb in opposition to the fingers is the chief key to our success in the use of tools, and the development of the hand and brain has progressed together. Compare the hand with the foot as to functional differences in both cat and human. Compare the functional relationships of the digits in cat and human. The pelvic appendage Pelvic girdle. The girdle of the pelvis in the adult is formed by tvm irregularly curved bones. These are the paired innominates, which unite rather firmly with the sacrum dorsally, and with each other ventrally, to form a ring through which pass the outlets of the alimentary canal and genito-urinary system. The shape of the pelvis is further adapted for numerous muscle attachments and especially in man serves as a partial supporting base for the abdominal viscera. Each innominate arises from three separate elements embryologically which extend to a focal point for the articulation of the thigh bone, or femur. At this juncture is a deep concavity for femoral articulation known as the acetabulum. The three elements are (1) the ilium, which extends most cranially and dorsally, and (2) the pubis, meeting the ilium from below and in front. These two form the cranial rim, or margin, of the pel~is (3) the ischium, which meets the other elements frqid behind and below.

53 THE SKELETAL SYSTEM 47 In the cat the ischium and pubis on either side join in the midventral line to form a fibrocartilaginous connection, the ischiopubic symphysis. Only the pubes in the human unite to form a symphysis. The separateness of the elements of the innominate bone are still evident in a kitten, but in an old adult they are so completely fused as to be indistinguishable from each other. The pubis and ischium surround a large oval obturator foramen. The ilium bears on its Femur ---_- / / / //,... Articuldtion ot fibula / / ' /' FIG Bones of the pelvic appendage, man and cat. (By John F. Trainor.) inner margin a rough articular surface where it joins the sacrum, and the entire girdle is but slightly movable as c'ompared with the pectoral. The human pelvis varies to a considerable extent in the two sexes. Both diameters of the pelvic opening are relatively greater in the female, particularly the dorsoventral diameter, making the outline more circular. In the female, the pubic angle is also less acute than in the male. This is to accommodate the birth canal. In the cat, as well as in man, there is a tendency of less complete union

54 48 FUNCTIONAL ANATOMY OF THE MAMMAL at the symphysis of the female. Compare the pelvis of the cat and human as they would appear in a "sitting position," and determine which is better adapted for this position. The femur. This is the thigh bone and is rather freely movable. It bears a conspicuous ball-shaped proximal head and a rather long neck, which serves to set the bone well out from the body. The C rest of iii u m ) Ischial +uberosi Obturator foramen Ischiopub,ic symphysis F IG Pelvis of the cat. (Modified from Mivart.) proximal end is further characterized by the greater trochanter as a dorsolateral extension and a lesser trochanter below and caudally. A rather conspicuous intertrochanteric ridge extends from one to the other. A deep trochantic fossa is formed between this ridge and the neck. An oblique, slightly elevated ridge forms a linea aspera on the caudal margin of the shaft. A slight pit will be noted on the medial surface of the head which acts as an attachment point for the ligamentum teres, which helps hold the head in the acetabulum. The distal head of the femur bears.a pair of smooth articular surfaces, the internal (medial) and external (lateral) condyles between which is the trochlea, or intercondylar fossa. At the upper margin of each condyle is an epicondylar tubero!lity which the fossa. extends around in front to allow for the kneecap, or patella, articulation.

55 THE SKELETAL SYSTEM 49 The tibia. The large shank bone, or tibia, articulates with the femur- by means of tibial condyles bearing the same name as those of the femur. An intercondylar notch separates the condyles. Because of their concave character, the term "fossa" seems more applicable than "condyle" here. The cranial margin of the tibia below the head bears the prominent tibial crest which is affected in "bumping the silins." The caudal margin of the tibia is marked by Great trochanter Head Pit I ntertrochanh!ric fossa rntertrocha nteric Crest lined as~era Patellar.fossa Adductor (med) tubercle Medial condyle FIG Femur of the cat (cranial and caudal aspects). lateral condyle lntercondylar fossa (Modified from Mivart.) a deep groove separating two ridges. Tuberosities occur on the external and internal surfaces as well as above the crest. The distal head is prolonged into a medial, or internal, malleolus, the projection of which is called the pyramidal process. The distal end is deeply grooved for articulation with the talus (astragalus) of the tarsal series. The tibia is the longest bone of the cat skeleton. The patella. The kneecap at its upper margin is embedded in the tendon of the rectus femoris muscle. Its lower surface is combined with a ligament joining the crest of the tibia at its proximal end. As a sesamoid bo~e, the k~eecap is unique in size and importance. Its upper end is the broader.

56 50 FUNCTIONAL ANATOMY OF THE MAMMAL The fibula. In relative proportion, the fibula is the most slender bone of the body. It is placed on the lateral surface of the tibia from below the knee joint to the tarsus. The proximal head is usually slightly more expanded than the distal head and is held to the head of the tibia chiefly by the external lateral ligament. The lower head bears a smooth articular surface on the inner side for Medial Med. tuberosity 'Proximal head of fibula Lateral malleolus ial malleolus Di sto I fa cet FIG Tibia (cranial and caudal aspects) and fibula of the cat. lateral malleolus (Modifi.ed from M ivart.) articulation with the astragalus. The external malleolus projects as a conspicuous knob or bony prominence on the lateral side of the ankle. Tarsal bones. Of the tarsal series, the calcaneum (or calcis) is by far the largest. It is the bone of the heel, and although the astragalus (talus) bears the weight from the tibia, the calcaneum is of great importance as a leverage bone for this articulation. Its free end receives the prominent tendon of Achilles from the large muscles of the shank. The lower medial half is deeply grooved for the articulation with the astragalus, while its lo~er end articulates with the most lateral cuboides of the second-row series.

57 THE SKELETAL SYSTEM 51 The astragalus lies medial to the calcaneum, is only about half its length, and possesses a characteristic trochlear surface for the articulation with the tibia. Lateral to the trochlea, the bone is grooved sharply where it joins the calcaneum for additional support. Its lower and inner surface articulates with the third bone of the first row series, the scaphoid (naviculare) of the tarsal series. Metatars es} ell n e i fo rm nto Hallux (vestiqial) FIG Bones of the hind foot of the cat. (Modified from Mivart.) The latter bone may be recognized by the deep concavity for this articulation. It serves as a key bone for the other six tarsal bones. The cuboid, previously mentioned, is the most lateral of the series of four in the second row of tarsal bones. It bears a deep even groove on its lower border through which passes the tendon of the peroneus longus muscle. Three cuneiforms follow toward the medial aspect. The external cuneiform bears a prominent hooklike process. The middle cuneiform, a wedge-shaped bone and smallest of the group, separates the external from the internal cuneiform, which '~s but slightly larger. From above, the internal cuneiform joins the scaphoid, and below it articulates with the first

58 52 FUNCTIONAL ANATOMY OF THE MAMMAL two metatarsals of which there are but four fully developed in the cat. Sesamoid bones of a variable character develop in the regions of both metacarpals and metatarsals. Metatarsals. The first metatarsal is extremely rudimentary in the cat, and there is no "big toe." The others are larger and stronger. The broader proximal end is called 'the base from which, extends a shaft ending in a rounded and somewhat constricted head. These bones ar~ not to be considered in the same sense as long bones,.' however, since each develops from a single ossification center. From the primitive standpoint, mammals characteristically possess five metatarsals as well as the same number of metacarpals. Each metatarsal of the four developed in the cat bears three,phalanges in the digits. Since the first metatarsal is vestigial, the phalangeal bones for it are missing. A stout, but not especially sharp, claw is borne on the distal phalangeal bones. Compare the phalanges of the cat with man, and note that claws and digits in the cat are more specialized than in man. Polydactylism, the presence of extra digits, is fairly common in both man and cats. It is a hereditary condition. An interesting example was seen by the writer recently. A pregnant female cat possessed six welldefined digits on the forelimb and five on the hind limb. The five fetal kittens taken from the uterus exhibited exactly the same condition of polydactylism. This indicates the dominant character of the factor. ARTICULATIONS Special dissection of joints is usually not attempted in general courses. \ \ If time permits, an examination of the typical articulations should follow. the dissection of muscles. Howev,er, because of the relations with skeletal study, a text descriptioi_l is given here. Articulations. Connections, or unions, between bony elements are known as "joints" or "articulations." These are classified on the basis of the range of movement permitted and the type of material interposed between adjacent bones. This material varies with the type or range of action allowed at the joint. Attachments and associations of muscles tend to aid greatly in holding the bony framework together, but the bones are more intimately bound together by the more direct and special ligaments. While it is the primary function of a tendon to afford efficient muscle attachment, ligaments are primarily important in holding the bones closely within the proper limits of their functional range. The use of the term "ligament" is not restricted to the structures at the joints. Supporting attachments of certain of the viscera are known by the

59 THE SKELETAL SYSTEM 53 same general term. Cartilages of the voice box (larynx) are also equipped With ligamentous structures that join them together. The vocal cords also represent specialized modifications of a type of ligamentous tissue. Ligaments, tendons, fascia, and aponeuroses are all related connectivetlli'i:\ue elements. Ligaments ~onta,in a, mme or les'i:\ a,bunda,nt 'i:\upply 01 elastic fibers which auow a controlled degree of mobility at the movable joints and thus differ from tendons, which are inelastic. The elasticity of ligaments, no doubt, prevents more serious injury to the joint in case of dislocations. Ligaments at a joint usually lie outside a lbpecial capsular ligamentous sheath that encloses movable articulations. The more specific structure of some typical articulations should be observed in a later dissection. Bones of the cra.nium are joined by means of sutures, allow for no movement, and possess a cementing substance between them. Since the bones. of the cranium are functionally concerned with protection, they vary in size, shape, and thickness, depending upon their use at their particular position. Many of these unions are strengthened by interdigitating edges. Interosseous 1i9amen-t A Go Lateral and Tibio-fibul Lateral and liqoments capsular li9aments Fibula In terosseou Jiqament FIG The elbow (A ) and knee '(B ) joints of the cat. B (Modified from Mivart.) The centra of the v~tebrae are contacted by means of fibrous cartilage and are particularly concerned with carrying weight. The movement is slight between any two vertebrae, yet the combined column may curve considerably. The intervertebral disks of fibrocartilage also act 'to prevent jars along the axial skeleton. The articular processes of vertebrae lend additional strength to the column, and these move rather freely upon each other. Where free moverr1ent is common as between the long bones, the articular surfaces are smooth and consist 01 hyaline cartilage. The heads 01 the'

60 54 FUNCTIONAL ANATOMY OF THE MAMMAL bones are expanded to afford strength at the joint and to allow for more elaborate ligament attachments. The freely movable joints are each completely encased in a sheath of fibrous tissue known as the capsule of the joint. The inner lining of the capsule is made up of a glandular epithelium, or synovial membrane, which secretes the lubricant synovia, a fluid about the consistency of fresh egg albumen. Ligaments lie to the outside of the capsule, although there are instances where tendons. pass through the capsule. Outpushings <if synovial membranes to form closed sacs are known as bursae. These are common at joints between surfaces likely to be irritated by friction of moving parts, as skin over a bone or joint or muscles over bone. Special sheaths of tendons also serve as accessory ligaments passing over a joint. These are similar to bursae and facilitate the movement of the tendon past the joint or joints. The 10rm 01 heads or epiphyses of the long bones usually determines the degree of action permitted at their joints. Thus the olecranon process of the ulna not only prevents its overextension at the elbow, but also prevents its rotation in either direction when it occupies the fossa of the humerus. I In other types of bones the articulating substance and ligaments are more concerned with their freedom of action. Classes of joints Types of articulations are classified into three major groups, each of which contains several subclasses. The principal classes are (1) freely movable,. or diarthroidal; (2) slightly movable, or amphiarthrodial; and (3) immovable, or synarthrodial, joints. Diarthroses The subclasses of diarthrodial joints are distinguished" by the type of free movement permitted. The joint surfaces are covered with the articular cartilage enclosed in the synovial membrane and connected by ligaments. The union of the atlas and axis allows for limited rotation and is known as a pivot joint. The articulation of the proximal head of the radius with the ulna is also of that type, although the bony make-up is quite different. The hip and shoulder joints not only allow for rotation, but also permit a rather free movement in all directions. The spherical head of the long bone articulates in a cup-like depression of the girdle bone. Such a joint is known as a ball-and-socket, or enarthrodial, type. Condyloid joints allow for abduction, adduction, flexion, and extension but not rotation. The union between the metacarpals and phalanges is of this type. In the thumb of man, however, there is a modification in the carpometacarpal union in which the articulating surfaces are each saddleshaped and fit into a reciprocal reception. Gliding joints allow for a limited gliding action of two flat surfaces, as the articular surfaces of the processes of vertebrae (zygapophyses). These.

61 THE SKELETAL SYSTEM 55 articulations are most free in the cervical region and least free in the thoracic. The capsular ligaments are supplemented by ligaments connecting the lamina of the vertebrae. These are particularly well developed in the neck region to form the ligamentum nuchae which contains abundant elastic fibers and extends to the head. These ligaments assist the muscles in movements of the spinal column, and the neck ligament in quadrupeds gives considerable support to the extended head. The hinge joints, or ginglymus type, permit flexion and extension only. The elbow and knee joints are typical. It is well to recav, however, that at the elbow particularly where three bones are involved there are two types of action. The rotation of the radius with the ulna at the humerus allows for pronation and supination, while the articulation of the ulna with the humerus is purely a hinge joint, allowing only for flexion and extension. Amphiarthroses This class allows for only slight movement. The articular surfaces of the bones are of cartilaginous material and are held in close proximity by ligaments. Joints between the centra of vertebrae are typical. The ischiopubic symphysis belongs to the general class, but in this case the union is more firm. In old males the symphysis more closely resembles a suture. The sacro-iliac joint also belongs to this general class. Synarthroses As previously mentioned, the sutures of the skull are immovable unions and are typical of this type of articulation. In an immature long bone the epiphyses are likewise joined to the diaphysis, later to become diaphysis by the replacement of intervening cartilage with bone. Obviously, more muscles are involved at joints where free movement is permitted. These muscles serve not only in movement of parts, but are also functional in protecting the joint from injury by being in a "tonic state." This muscular tenseness, or tone, serves as "muscle sense" in preventing dislocations in case a sudden or unexpected force acts upon the joint. In the dissection of muscles, it will also be noted that tendons are attached in a manner to prevent slipping of the joints. For example, the contraction of the biceps brachii not only produces action at the elbow joint, but also tends to pun the head of the humerus into the glenoid fossa. At its point of insertion on the radius, it aids in holding the capitellum of the humerus and the radius together. LEVER SYSTEMS The significant feature of joints of the movable type rests in the arrangement of the bones tij serve as levers. Although the mechanical principles are obvious, certain of the arrangements are extremely complex and diffi-

62 56 FUNCTIONAL ANATOMY OF THE MAMMAL FIG Ways in which the foot may be used, involving the leverage principle. In class I the foot is lifted and the toe is used to move a resisting force W backward. II shows the u se of the foot in lifting the body on tip-toe. If the true fulcrum is at F, and the weight Wand power P are as mdicated, this illustrates I, class II lever. However, the weight appears to be shifted to the toes to cause the ankle to also act as a fulcrum as in class I. In the class III lever, the power is applied between tbe weight and the fulcrum. Humerus Distance of pull Distance throu9 h which wei9ht is lift"ed at the wrist FIG An example of a leverage system lidapted for the production of speed rather than strength. The lever arm here is relatively short (from F to P which greatly reduces to power advantage, but by operating through Ii short distance P-P the resisting force W is moved relatively far W-W. This class III prirlciple is most common in the body.

63 THE SKELETAL SYSTEM 57 cult to describe in terms of mechanics. A lever, in simple form, is a rigid bar that can be employed to gain mechanical advantage against a resisting force or weight. For example, in moving an object that is too heavy to lift directly, we apply a lever. Also a lever may be employed to increase velocity; for example, a ball in the hand passing in an arc in a throwing motion is traveling at much greater speed than one attached to the upper arm during the mot~on. B C Prono..tion. SupinC'l.tion FIG Pronation and supination of the hand and the location of the muscles performing these apposing actions. Note the leverage principle in the rotating radius. (From Millard and Kino, "Human Anatomy and Physiology.") The essentials of a leverage system are (1) a fixed point for the lever to act against, the fulcrum, (2) a power to move the lever around the fixed point, (3) a resisting force or weight to be moved. In the body the fulcrums are located at the joints, power is supplied by muscles that attach to bones by tendinous connection: the resistance may be merely moving a part against gravity. Three classes of levers are described with reference to the relative positions of these features of the system. Authorities differ as to whether all three classes operate in the body. The foot illustrates the mechanical principles, as shown in Fig

64 58 FUNCTIONAL ANATOMY OF THE MAMMAL Simple leverage is not common in the mechanics of the body. For example, the proximal tendon of the biceps brachii passes through the shoulder joint somewhat like a rope is passed through a nonrotating pulley, thus involving the joint there. The muscle forms a belly near the middle of the humerus, then continues as an inserting tendon across the elbow joint to attach at some distance below the joint on the radius. This attachment is rotated with the radius when the hand is pronated or supinated, causing the tendon to wrap itself partly around the radius in pronation. Although the elbow joint. is chiefly affected by the power of contraction, the effect is not simply one producing flexion, but the force also is applied to produce rotatory movement. Difficulties are likewise encountered in interpreting the character of the lever in standing on tiptoe, usually described as a class II lever. Here the body weight is shifted from the ankle to rest upon the toes, which may also be considered the fulcrum. In this interpretation the resistance is the surface to which the foot is applied, and the lever is essentially similar t~ A or class I. Most of the levers of the body are of class III type, which are more effective in developing speed than efficient in lifting weight.

65 Chapter III SUPERFICIAL DISSECTION OF THE CAT GENERAL dissection is usually done on specially prepa~ed material. Most laboratories use animals that have been embalmed with a solution of glycerin, phenol, formalin, and water injected into the femoral artery. Following the embalming fluid, a colored mass (preferably latex) is injected into the same artery which fills all the systemic arteries, the left side of the heart, and the pulmonary veins. A mass of blue colored material is usually injected into the veins so that the vessels may be easily distinguished and traced. The venous injection is usually not so complete as the arterial because the lining of veins possesses valves that tend to prevent flow away from the heart. These preparatory procedures cause considerable change in the texture. color, and general appearance of the tissues from the living condition. Superficial characters and landmarks A male can be distinguished from a female most readily by the possession of a scrotal sac containing the testes. The scrotum lies just ventrad to the anus as a prominent bilobed projection. The penis is rather deeply retracted between the testes and is directed ventrocaudad. The absence of testes does not always denote a female specimen since castrated males are not particularly uncommon in laboratories. Other superficial characters should be noted, but these are commonly so well known as to warrant an omission of detailed description here. Since preservatives harden the tissues and alter the general pliability of the body, some of the bony landmarks are best determined on a live animal or on one freshly killed. Such features as the spinous processes of the vertebrae, crest of the ilium, the spine and acromion process of the scapula, angle of the ribs (costal angle), etc., should be located by forceful pressure of the fingers. Also hold the specimen in an upright position, and orient landmarks in relation to their position in your own body. Note particularly the position of the heel, wrist, elbow, etc. Observe the general shape of the body and the relative proportions of head, neck, trunk, and tail.. 59

66 60 FUNCTIONAL ANATOMY OF THE MAMMAL Dissection of the skin Perhaps the best method of a laboratory dissection of the skin of the cat begins with a longitudinal incision in the middorsal line over the sacrolumbar region. A shallow incision 2 or 3 inches long should first be made. This should be carefully deepened until the skin has been penetrated. This can be determined by probing the edges of the incision. The skin can now be loosened from the underlying tissues by inserting the fingers into the incision. Care should be taken to cut no deeper than through the skin, particularly between the shoulders. By loosening the skin in front of the incision with the fingers, it can be pulled free well over the front of the head and back to the first three or four caudal vertebrae. Underlying the original incision is a broad expanse of tough white connective tissue, the dorsolumbar aponeurosis. A smaller expanse of similar tissue lies between the vertebral borders of the scapulae, the trapezius aponeurosis. These tissues should not be damaged since they serve as muscle attachments. As the cut edges of the skin are pulled laterad, white threads, the cutaneous nerves, will be seen to extend from the body to the skin. These are obscured by superficial fascia, or loose connective tissue, which aids in binding the skin to the underlying parts. Note that the cutaneous nerves occur at regular intervals, indicating the position of the spinal nerves of which they are branches. The distribution of the cutaneous nerves indicates the original segmentation of the embryo, and functionally the skin is segmentally divided into rather distinct bands of sensory areas corresponding with the nerves. These are the most superficial of serial homologues in the mammal. Following the course of nerves will be seen the larger cutaneous arteries supplying the skin. These vessels appear as red threads in an injected animal. Ordinarily, the cutaneous veins are difficult to see because the blue injection mass does not reach them. The skin should be pulled down along the sides of the body and kept intact as far as possible. Transverse incisions about midway may now be made through the skin, and by careful use of the scalpel it may be further removed. First follow the cranial portion. In the breast region, particularly, will be seen a thin layer of muscle fibers that remain with the skin. These are cutaneous muscles inserting to the skin and are used mostly in flicking movements perhaps seen best in horses when annoyed by flies. Where cutaneous muscles appear to be continuous with deeper muscles, they should be cut so as to leave them with the body rather than with

67 SUPERFICIAL DISSECTION OF THE CAT 61 the skin. These cutaneous muscles continue over the neck and bear much resemblance to the facial muscles of expression. The skin over the appendages, when free at their attachments to the body, will usually pull down as far as the digits, where it may be broken off. Around the neck and head the skin is extremely thick and tough, particularly in old males. This condition appears to be a protective' adaptation in combat. The caudal portion of the skin can be separated completely around the tail and the tail clipped off back of the third or fourth caudal vertebra. Carry the incision around the anus and external genitalia so as to leave these protected. Where such a portion is left in dissection, it is said to have been "spared." In the case of the tail and other skin removed, it is said to have been "sacrificed." These terms will be useful later. The skin of the hind appendages should be removed as in the forelimbs. With the removal of the skin, drying of the body is prevented by keeping the specimen wrapped in a damp cloth (unbleached muslin) frequently moistened with a solution of phenol, glycerin, and water. The student should assume the responsibility for keeping his specimen in good condition when proper materials are provided. THE INTEGUMENT AND ITs DERIVATIVES The in.tegument consists of the skin and the special structures that are derived from it. The superficial layer is a stratified epidermis, details of which must be studied microscopically. The underlying dermis is many times thicker than epidermis and is the part of the skin from which leather is made. As the skin is removed from an animal, some loose connective tissue comes free with it; this is hypodermis, or superficial fascia. Usually no attempt is made to dissect the separate sheets of fascia in mammalian dissection as in human dissection. In the cat, both skin and fascia are thickest over the neck and head regions. Note also that the skin at the distal parts of the appendages is also relatively thick. At these regions, it also adheres more closely to the underlying tissues or deep fascia, which helps form the covering of muscles. Although the hair follicles are imbedded in the dermis, hair is of epidermal origin owing to inpushings of this layer. Cutaneous nerves terminate j'lst at the point of reaching the epidermal layer, and the cutaneous blood capillaries also reach this level but do not penetrate the epidermis. The larger nerves and vessels (cutaneous

68 62 FUNCTIONAL ANATOMY OF THE MAMMAL arteries) will readily be seen where they have been broken off when the skin is removed, but their distribution must be studied microscopically. Portions of the skin that are devoid of hair are notably the "soles" of the feet and "palms" of the hands. At these points, where forceful contacts are made, the skin develops friction ridges. Note these on the pads of the cat's feet. These ridges represent thickened epidermis. It, is well known that a callus tends to form at any holr sho ff epidermis m alplghlon sebaceous (oil) gland dermis sweaf follide nerve F IG A diagrammatic cross section of the human skin. The blood vessels have been omitted. (Rooers, Hubbel, B yers, "}lian arui tm Bioiooicai World." Redrawn from Clendennino. ) point on the skin where continued and forceful friction occurs. This serves as added protection for the live underlying cells and represents an adaptable character. In many mammals, sweat glands are few or absent, and the nose tip is free of hair. This is supposed to aid in eliminating heat. Certain of the skin derivatives are of an extremely hardened character. The enamel layer of the teeth is similar in origin to skin derivatives and is the hardest of all parts of the body. Hoofs, nails, and claws are also examples of hardened derivatives. Claws of the cat are homologous with the nails of man. Examine these closely and determine which you would consider more specialized. The claws should then be clipped to prevent accidental scratches.

69 SUPERFICIAL DISSECTION OF THE CAT 63 The glandular derivatives of the skin that cannot be seen by gross observation are the sweat glands and the sebaceous, or oil, glands. There are many modified glands among the different mammals which are similar in origin but differ greatly in function. The mammary glands are of a compound character, possessing numerous branches terminating at a single nipple. In the cat, eight nipples are present, four on either side, distributed from the thorax to the pelvic region. This type of distribution is known as universal. Compare with other mammals. Mammary glands become greatly enlarged during functional activity. In the cat, those in the abdominal region are especially functional. The number of glands that remain functionally active corresponds to the number of suckling young, usually four or five. Peculiarly enough, the mammary glands are more closely related to the sweat glands in similarity of origin than to the oil glands. Oil glands are typically associated with hair follicles. The secretory portions are derivatives of the epidermal layer. The hair of mammals assumes definite hair patterns that vary among different groups. These patterns are not so obvious on the cat because of the dense nature of the fur. They are, perhaps, best demonstrated on pigskin gloves, where by close observation, without lens, one may make out the characteristic pattern, which is repetitious. The coarse bristles of the pig project well down into the thick dermis. On the cat, note the heavy bristles projecting well out from the lips. These are known as the vibrissae and are supposed to function as tactile structures enabling the cat to determine immediately whether the size of an opening will permit the passage of the body. In considering the skin and its derivatives as a whole, from the functional standpoint, the integument is most diverse. Such apparent unrelated functions as providing nourishment to the young, aiding in the maintenance of constant body temperature, and the provision of structures of use in defense and offense illustrate this point. Certain of the structures of offense are peculiar, as, for instance, the scent glands of skunks. Superficial dissection-fascia, cutaneous nerves, and vessels The connective tissue (fascia) may be first removed over the thoracic and neck regions. Fascia on the cat should be removed by blunt dissection, and no attempt is made to remove fascia intact. Except in extremely tough specimens, it is usually best removed by the fingers alone. The superficial skeletal muscles' are exposed by removing the fascia. Each muscle should be cleared of fascia sufficiently to make its exact limits readily apparent. Avoid picking at the muscle fibers, and do not attem~t to remove more fascia than is necessary to expose the separate muscles. It should be observed, by close exami-

70 64 FUNCTIONAL ANATOMY OF THE MAMMAL,-/ Trapezius ( -- I I mox;mus&med. I'. I I CCludo- I fe mor:o I is I T fascia 1"+(1 - -ope~ed to show ---Vostus laterali, -- - Biceps fejtloris insczrtion cut to show -:-.:::-"" Gostrocn~mius _- FIG Superficial muscles of the cat after the fascia has been removed. F. Trainor. ) -,--"j (Drawn by John nation of its fibers, that fascia tends to present a net-like appearancp.. Observe again the fascia-like binding between the shoulde.rs and over the lumbar region. This binding should not be removed. In these regions it will be noted that the muscle fibers thin out, leaving broad flat tendons as attachments. Such tendons are known as an "aponeuroses." These are superficially similar to ordinary fascia, but the aponeurotic fibers tend to run parallel to each other in layers. The dorsolumbar aponeurosis serve.j as a part of the fixed attachment of the broadest muscle of the back, the latissimus

71 SUPERFICIAL DISSECTION OF THE CAT 65 dorsi, which extends to the humerus. The trapezius aponeurosis serves to attach the right and left acromiotrapezius muscles with each other in such a way as to provide a free area between the shoulder blades (vertebral borders) which allows for their rotation. Observe a large superficial vein on either side of the ventrolateral surface of the neck, the external jugular. Carefully observe and remove. the connective tissue that partly obscures the vein, and note its passage posteriorly between two muscles; the one median to the vein over which it passes is the sternomastoideus, the one lateral and deeper is the c1eidomastoideus. Clear away the connective tissue. of these muscles up to the mastoid region of the skull. Facial Parotid gland uc'co 1 q land Inferior facia vel n Lymph nodes Submaxillary q land Ext ju9ular vein FIG Superficial dissection of the head of the cat. (Modified from Mivdrt.) Anteriorly and under the chin region, the two external jugulars form a union (anastomosis) from side to side by means of a transverse jugular. Trace the external jugular craniad to observe its formation by the union of facial veins. Note a rounded mass of tissue back of the angle of the jaw and under the sup erick facial vein, the submaxillary salivary gland. Also no~e a more irregular mass of the same sort of tissue at the

72 66 FUNCTIONAL ANATOMY OF THE MAMMAL base of the ear which is the parotid salivary gland. At about the point where these two glands come in contact at their forward margins may be seen the duct of the parotid (Stenson's duct), which passes forward directly over the largest jaw muscle, the masseter. The small lymph nodes which superficially resemble salivary glands may be seen at the lower border of the masseter, one on either side of the inferior facial vein and in contact with the submaxillary gland.

73 Chapter IV A STUDY OF THE VOLUNTARY MUSCLES ~HE special function of skeletal muscle is to supply the power for volun -\ tary motion and locomotion. Activity of these muscles produces heat as ~vell as movement, and most of the heat of the body is generated in the muscles to be distributed by the general circulation. Furthermore, muscular activity sets up a series of physiological events affecting the degree of activity of other body functions, notably respitation and circulation. Even at rest, the muscles are in a state of readilll~ss or tonus, and joints are usually held in a slightly flexed position. No other ti'3sues are under similar control through the conscious centers of the brain. Except in extraordinary situations, only a small fraction of the maximal muscular power is needed. The muscular system really consists of a series of functional groups of muscles which may act independently, concurrently, or in sequence in performing a comple:x: coordinated exercise. The great amount of muscular tissue present and its capacity for doing work is of particular advantage during short critical periods. This fact is important in circumstances of combat or in escaping from enemies or in other situations that demand temporary bursts of m!}'ximal energy. No mammal can maintain its maximal output of muscular energy for more than a few minutes. The limiting factors of exertion are principally found in the inability of the respiratory and circulatory sy13tems to supply oxygen and remove wastes rapidly enough to prevent mu.scular fatigue and complete exhaustion. In mammals generally, skeletal muscles make up about half the total weight and bulk of the body. Between 450 and 500 different muscles may be recognized in man, and approximately thfl same number occur in the cat. Almost all these are duplicated in coni'ormation with the bilateral symmetry of the body. Some are repetitiou~ to conform with the serial arrangement of the vertebrae and ribs. In the hand and foot, most of the different muscles are also somewhat duplicateld on the various digits in a radial manner. The muscles that are concerned with movements of the appendages are known as appendicular muscles. Those which have no attachments to either of the appendages make up the intrin;ic axial musculature of the head, neck, thorax, and abdomen. 67

74 68 FUNCTIONAL ANATOMY OF THE MAMMAL The cutaneous, or skin, muscles These thin sheets of muscular tissue that attach to the skin were mentioned in connection with superficial dissection. The cutaneous muscles will not be considered here in any detail. After a specimen has been skinned, the remaining portions of integumentary muscle fibers must be cleared away with the fat and fascia. On the skinned specimen, usually a thin flap of skin muscle adheres to the 'underlying musculature over the back of the neck. This is a fragment of the platysma, most of which was removed with the skin. Another such remnant may be found just behind and above the axilla, or armpit. This, the panniculus camosus, also merges closely with the deeper muscles from which it arises. The platysma is sometimes considered as an anterior extension of the panniculus. The muscles of facial expression are similar to integumentary muscles. They should be observed when the skin is removed from the head. Structural features of a skeletal muscle From a purely morphological standpoint, each living muscle is an organ consisting of representatives of each of the five fundamental types of tissues. The dominant and most abundant tissue consists of striated muscje fibers arranged in bundles (fasciculi) and surrounded by sheaths of connective tissue. On the surface of most muscles, the connective tissue forms a thin enveloping cover known as epimysium. Internal extensions of the epimysium divide the muscle into bundles of fibers. The superficial muscles are also largely interconnected along their margins with deep fascia, which is a dense tough extension of the loose superficial fascia that binds the skin \ to underlying parts. Another type of connective tissue, consisting principally of strong inelastic fibers, is present at each end of the muscle. This white fibrous tissue may converge into a compact tendon; it may form broad tendinous sheaths previously described as aponeuroses; or the fibers may appear to attach directly to the periosteum of the bone without forming concentrated tendinous connections. All tendons are attached to the periosteal sheaths of the bony framework; the periosteum is joined firmly to the bone by minute fibers (fibers of Sharpey). In addition to muscular and connective tissues, close examination of a muscle reveals a distribution of nerves to each muscle. Microscopic examination reveals that each muscle fiber receives a neurofibril of a motor nerve, and sensory fibrils are richly distributed near the tendinous attachments. Each muscle receives a blood supply and drainage, thus possessing vascular tissue. The blood vessels are lined with a special type of epithelium (endothelium). Therefore, an isolated muscle may be de~cribed as a more or less independent organ. However, under actual working conditions, each

75 A STUDY OF THE VOLUNTARY MUSCLES 69 muscle must be considered merely as a unit of a functional group in understanding its true character. The central nervous system recognizes and controls movement rather than individual muscles, and we should attempt to study muscles from this standpoint. Functional features of skeletal muscles Certain other features are common to each of the skeletal muscles, regardless of their particular location, size, or general form. These features must be kept in mind, and constant reference must be mad~ to the skeletal system while muscles are being studied. (1) Each muscle does its work only by contraction or shortening of its fibers. Its maximum contraction terminates its usefulness in doing further work until the fibers have again elongated by opposite force of an antagonistic muscle. (2) The fibers must be attached by inelastic connections (tendons) to two different parts of the bony framework with a movable joint or joints between the attachments. (3) The type of action at a joint depends primarily on the exact positions of the attachments on the framework, the functional axis being between the attachments and along the direction of the fibers. (4) The bony framework on either side of the joint is affected differently by the pull of the muscle; the framework on one side of the j oint remains relatively stationary, while the skeletal part on the other side is drawn or moved toward the stationary part. Thus, the movable bone or part is pulled like a lever with the joint acting as a fixed point of the lever (fulcrum) around which the lever bone moves. The relatively stationary attachment of a muscle is known as its origin, the movable point, the insertion. Because of these features, muscles work in antagonistic groups. For example, while the muscles of one set are undergoing contraction, producing a bending action (flexion) at a joint, they are considered as protagonists, and their antagonists (the extensors) are being stretched preparatory to performing the opposite action. Other muscles are used to guide a principal action within the desired planes and to limit the activity. These are known as synergists. Thus, one understands the actions of muscles not only by studying the line of action between the two attachments (origin and insertion), but by studying opposite lines of actions and the modifying influences of synergic groups. Although muscles are commonly described as isolated units, they do not act as such, and the simplest activity as picking up a pencil not only involves a large number of muscles but a complicated sequence of coordinated actions. Anatomical position and muscle actions Types of actions possible at joints were originally described for man as beginning from the anatomical position of standing erect with the arms at the sides and the palms of the hands facing forward (supine). This position would not only be unhatural for the cat, but would be impossible to imitate closely without distorting and dislocating the normal arrangement of the

76 70 FUNCTIONAL ANATOMY OF THE MAMMAL bones of the thoracic appendage. Therefore, an attempt to describe the muscle actions of the cat by exact terminology applied to human dissection leads to much confusion. Most of the difficulties encountered in comparing conditions in the cat and man are not in homologizing the parts (seeing the structural similarities), but in attempting to make functional analogies. These difficulties are traceable to (1) the use of the forelimb of the cat in support of the body and in locomotion, (2) the bilateral compression of the body and consequent position of the scapula, and (3) the reduction of the clavicle so that the brace effect of the bone in man is lost in the cat. The clavicle is entirely absent in the hoofed mammals, a condition that contributes to greater mechanical efficiency in the extended stride and reach of the forelimb. In walking on all fours, man is not only handicapped by interference of the clavicle in the forelimb stride, but he also has difficulty in keeping the arm directly under the body. Since the forelimb of the quadrupeds supports a considerable portion of the body weight, the supporting bones of these animals must be kept more directly under them to relieve strain at the joints. This position has not been well achieved in amphibians or even in the reptiles whose elbmys are directed laterad as well as backward. Since man is free from the necessity of using the arms for body support, he possesses a considerably greater range of action of the thoracic appendage than does the cat. To achieve the greater range of action in the arm of man, the breast muscles passing from the sternum to the humerus attach relatively high, whereas in the cat these breast muscles hold the humerus close to the body by inserting on more than half the length of the bone. This fact leaves only a small part of the upper arm free of the body. Little more than the elbow of the horse is visible externally, since the breast muscles are even further developed here than in the cat. One of the problems of comparative mammalian anatomy that appears \, to have received inadequate attention concerns the evolution of the position of muscle attachments, and consequent effect on their actions, from the quadruped condition to the biped condition in man. A study of the muscular system of the cat should be made from a comparative functional standpoint. For example, in paralysis of man, due to nerve injury, each muscle or group of muscles affected IS considered from the standpoint of efficient functional connections and favorable anatomical positions in doing work. Nerve injury in man may immobilize the arm only so far as extension is concerned, with the arm hanging at the side in normal anatomical position for man. Yet, if the arm of such a patient is placed in a primitive position, i.e., partly extended, the paralysis may be overcome and further extension may be effected voluntarily from the more favorable position. Thus, reeducation of muscles that are partly paralyzed from nerve injury is largely based on a knowledge of efficient anatomical positions from which only small amounts of muscular energy are required to produce an action. In many instances, the position in which a muscle may work most effectively in man corresponds with the normal anatomical position, not of man,

77 A STUDY OF THE VOLUNTARY MUSCLES 71 but of the quadruped mammals. Therefore, a knowledge of more primitive mammalian conditions is valuable in this connection. A PRACTICAL STUDY OF MUSCLE ACTIONS IN MAN A systematic survey of the mechanics of the skeletal system should precede a study of the particular or specific muscles concerned with the various., Peroneus lon~us Xt..di~ito('um lon~us., FIG Superficial muscles of man. Anterior (ventral) view. (Millard and Kino.. Huma'", Anatomy and Physiology.")

78 72 FUNCTIONAL ANATOMY OF THE MAMMAL Extensor dis3,itorurn communis G:tissimus dorsi Gastroc nenuus FIG Superficial muscles of man. Posterior (dorsal) view. (Millard and King, "Human Anatomy and PhYsiology." ) actions. This study involves a review of the functional character of each of the joints or parts affected by muscular pull. Many of the mechanical aspects of muscular actions can be learned by the use of mounted skeletal material and artificial models, but the student should perform the actions himself on his own body. This procedure is not only valuable in clarifying. definitions, but is essential in obtaining a more correct view of actual conditions and functional limitations of muscles which cannot be adequately. or properly learned from nonliving material. Note, when possible, the

79 A STUDY OF THE VOLUNTARY MUSCLES 73 location of muscles that appear to contract in performing the various actions. The type of action produced by a single muscle is frequently complicated and may be compound. These complications occur because (1) a muscle may pass over and tend to affect the position of the bones at more than one joint; (2) it may be divided into different parts, each of which may have a somewhat different type of action on the joint; (3) the line of action may be modified by the tendon passing around a bony process or through restricting ligaments; (4) or the muscle may work effectively only when other parts are in certain anatomical positions. For instance, flex your forearm strongly,,,ith the hand supine, and observe your biceps. Now, in the same flexed position, turn the 'hand to the prone position and observe that the biceps becomes stretched rather than contracted. With the hand prone and the elbow flexed, the biceps acts only as a supinator of the hand; whereas with the hand supinated and the elbow joint extended, the biceps is essentially a flexor. The actions of the thoracic appendage are more complex than those of the pelvic appendage because the thoracic girdle is movable with respect to the axial parts of the skeleton, whereas the pelvic girdle is closely fused with the sacral vertebrae (sacro-iliac joint). Furthermore, the greater freedom of action in the wrist and hand requires more complex muscular equipment than is found for the ankle and foot. The most proximal movable articulation of the pelvic appendage is at the hip joint. In man, the clavicle of the thoracic girdle articulates directly with the scapula and sternum and serves as a strong cross brace between these bones. Hence the thoracic girdle articulates directly with the sternum but not with the vertebral column. The scapulae are held close to the vertebral column entirely by muscles, and the thoracic girdle therefore has a considerable range of movement conforming with the muscular attachments. Actions at the thoracic girdle The muscles that effect changes of position of the girdle are quite exten-,.'live; they possess broad origins on the axial skeleton and insert to the scapula, clavicle, and humerus. As suggested above, these muscles are concerned with two distinctive functions: (1) they serve to hold the thoracic girdle within a limited range of movement with reference to the axial parts (skull, vertebral column, ribs, and sternum), and (2) they tend to move' the appendage more or less as a whole, rather than moving some division of it as a unit. The muscles producing these movements are said to be extrinsic appendicular muscles, since one attachment is not on the appendage. Six primary actions are performed by the group. Each of the actions described below should be performed by the student on his own body. 1. Pull the scapul!1e toward the head (elevation of shoulders in man). 2. Pull the scapulae caudad (depression), a relatively passive action in man. These two actions occur in shrugging the shoulders.

80 74 FUNCTIONAL ANATOMY OF THE MAMMAL 3. Draw the shoulders backward (abduction), which pulls the arms apart or away from the midventralline and pulls the vertebral borders of the two scapulae together. 4. The opposite action is adduction, drawing the shoulders together in front as in clasping arms. 5. Rotate the scapulae backward, which results in a forward upsweep of the arm. In man, the arm is carried to a front horizontal position before the scapula begins to rotate backward; in the cat, the normal standing position is alm9st equivalent to the horizontal position of the humerus in man. 6. Forward rotation of the scapula results in swinging the arm backward or in pulling the body forward in crawling. A partial combination of these actions produces a more complex circumduction of the shoulder, which involves moving the entire shoulder in a circular manner around an imaginary fixed axis. This is sometimes erroneously referred to as rotating the shoulder. Note that an upward thrust of the arm produces a general lowering of the shoulder and a backward thrust causes an elevation of the shoulder. This change in the height of the shoulder is partly due to the triangular shape of the scapula and the shift of position of the angles during rotation. However, some true elevation and depression of the scapula does occur with rotation, and actions are frequently of a multiple character. Intrinsic actions of the thoracic appendage The intrinsic muscles of an appendage have both attachments on parts of the appendicular skeleton and are, therefore, integral parts of the appendage. Four general groups occur when classified on the basis of the principal position of their action: (1) those moving the humerus at the glenoid fossa of the scapula; (2) those affecting the position of the radius and ulna with respect to the humerus at the elbow joint; (3) those moving the wrist, (carpal and metacarpal joints); and (4) those working on the digits (phalanges). Movement of the humerus. The articulation of the humerus with the scapula is of the ball-and-socket type, permitting a wide range and combinations of actions. The primary actions are (1) lateral rotation, (2) medial rotation, (3) extension, (4) flexion, (5) abduction, and (6) adduction. 'Lateral rotation of the humerus occurs to a considerable degree upon turning the palm up (supination), and medial rotation occurs in turning the palm down (pronation) with the elbow joint extended. Extension and flexion of the humerus refers to swinging the humerus directly craniad and caudad in a striding motion. These motions bring the humerus in line with the long axis of the scapula (extended) and bent upon the scapula (flexed), respectively. Abduction refers to drawing the humerus to a side horizontal position; adduction is the opposite action. Thus, the normal anatomical position of the cat is with the humerus mostly extended and in man with

81 A STUDY OF THE VOLUNTARY MUSCLES 15 the humerus hanging flexed upon the scapula. In the quadrupeds, as previously indicated, the humerus is closely bound to the body by heavy breast muscles which tend to strengthen the humeroscapular joint but which considerably limit the extent of the actions compared with the col1- d.\t\ol\'i', \l\ ffi'(\,l\, i.e., tb.~ ~'(\,t ~\)'u\.d. l\o\' 'il,~,,'(\,\'~b. \'b.~ b'(\,~k 0\ \\,'il, l\~~k. Movement at the elbow joint. With the humerus relativel1 fixed in position, the radius and ulna are made to move at the elbow. However, in activities such as chinning a bar, the humerus is flexed upon the forearrn. The actions of the ulna are those of a hinge producing exten$ion and flexion of the forearm (ttntibrachium) on the humerus. The olecranon process fitting into the fossa of the humerus prevents hyperextension or backward bending of the elbow. The radius, however, acts also in a rotatory manner, articulating at the side of its articular head with the ulna at the radial notch and at its upper surface with the capitulum of the humerus. The rotation of the radius produces most of the supination and pronation of the hand. These positions of the hands may occur independently of the rotations of the humerus, as can be determined by grasping the upper arm firmly and working the elbow to produce pronation and supination. Lateral rotation of the humerus as well as of the radius, however, contributes much to complete supination of the hand. This is a condition of distortion in quadrupeds.. Actions at the wrist. The actions at the wrist are of four types: (1) flexion, (2) extensioil, (3) abduction, and (4) adduction. In standing on tne hands, the wrists are overextended, or dorsiflexed. Abduction at the wrist ln man reters to beno.mg the hano. outwaro. at the wtist with the ha [Iu supine, and adduction means bending the hand in toward the body. Since in the cat a completely supine position of the hand is abnormal anatomically, the same sort of action would be impossible to reproduce or imitate as described for man. Actions of the digits. The most powerful muscles acting on the digits are located on the forearm and possess long tendinous extensions over tne carpals and metttcarpais to reach the phalangeal bones. Other muscles working on the phalanges are located entirely within the hand. The later group will not be described. Their principal actions are abduction and adduction of the digits, with some others assisting the more powerful flexors in perforrning delicate graded movements. These are located on the inner surface of the forearm. The tendons of the extensors of IDe digits are located on the back of the hand. In the cat, the claws are retracted by special musculotendinous connections. Other actions. Most of the actions described above apply also to movements in other parts of the body and need not be redefined further when used in connection with them. Two additional terms are used for actions of the foot: inversion for "toeing in," and eversion for "toeing out." Frequently actions can ge better described in general terms such as "pulling the scapula dorsocraniad" or "bringing the arm to a side horizontal posi- 82 76 FUNCTIONAL ANATOMY OF THE MAMMAL tion." In these cases, it is better to use a simple descriptive sentence than to use some term, the meaning of which may be obscure. Further emphasis should be placed on the circumstance that any simple activity requires the use of numerous muscles and a series of coordinated actions. Changes in posture produce differences in gravity effects, and compensating move-. ments are instinctively made in balance and equilibrium. Thus, walking involves a constant use of muscles other than those principally engaged in \ propelling the body forward., The naming of muscles Originally, muscles were described in long Latin sentences. For convenience, these descriptions were later cut down to a few words that were most applicable to the muscle concerned. Muscles are named chiefly in relation to (1) size, (2) position, (3) general shape, (4) points of attachments, (5) action, and (6) number of heads, or from a combination of these factors. Since comparative anatomy had its background in human anatomy, many structures described for man differ considerably in the cat, and many of the terms are not quite so applicable in quadrupeds generally, although the homology may be clear. The biceps brachii is so named in man because it attaches to the scapula by means of two heads and passes over the brachium, or upper arm. In the cat, its homologue is readily apparent; yet here it attaches to the scapula by a single head. Likewise, the muscle homologous to the rhomboideus major of man is easily determined in the cat, but it is the smaller of the two divisions of the rhomboideus in the cat. But because of the origin of the name it is retained in relation to the minor. An example of a muscle that is constant for the cat and anomalous for man is the rhomboideus capitus (occipitoscapulfl1is), which extends from the occipital bone of the skull to the scapula. This is not a good name for the muscle because in the human, where it rarely occurs, it is considered as a slip of the rhomboideus group and is known as the rhomboideus capitus. A translation of names is particularly helpful in recognizing and remembering muscles. Thus, when the extensor carpi ulnaris brevis is translated into the short extensor of the wrist on the ulnar side, it is more easily identified and under-. stood than if it were given a name of no particular significance. Comparatively few muscles occur in the cat which are not represented by homologues in man. In general, a remarkable uniformity of position and form occurs. With all the differences in locomotion and functional levels, the circumstances of so much similarity seem more impressive than that certain distinct differences do occur. Method of muscle dissection The general method of dissection presented here is designed to allow for but one specimen to serve for a study of all the systems. Since the connective tissues function in binding all other structures 83 A STUDY OF THE VOLUN'l'ARY MUSCLES 77 together, the major work in dissection is the removal or separation of connective tissues. This should not be done as a mechanical routine, but by careful analysis of functional connections. Few rules in muscle dissection are to be observed, but those rules are important. The deep muscles must be exposed by transecting the more superficial. ones and reflecting the cut edges. A transection should be made only after careful study of the superficial characters of the muscles under consideration. Th~ dissection should be made so that but one muscle is cut at one time. Therefo~e, the boundaries must be accurately known. The transection should be made about midway between origin and insertion in most cases. By following this procedure neither the origin nor insertion is cut into, and it is possible to replace the cut edges for later observations of the trsmsected muscle.in.its or.ig.imj pa.,«.itjd.1;l. 'The middle portion of a muscle is usually relatively free from large nerves and blood vessels so that danger in cutting these is pra,ctically eliminated. Each muscle is to be reflected to its points of [tttachments, but not necessarily immediately after transecting. Frequently, the attachments are obscured until further transections of other muscles are made. It is assumed that the student may further work out a method of approach to underlying parts with little additional preliminary instruction. In reaching the termination of tendohs it is sometimes difficult, or impossible, to preserve the innervatioh and blood supply without distracting too much from the muscle study. One side of the body may be used primarily for muscle dissection, in case precise origin and insertion are to be determined, while the other side may be used for a study of the details of nerve and vascular relations to the known muscles. Close observations should be made of the association of muscle, tendon, periosteum, and bone. The periosteal covering of the bone should be observed in fresh material, if possible. A "pulled tendon" infers that its connection with periosteum and bone has been disrupted, An unusually forceful (~ontraction may result in this, or injury may affect the muscle fibers to cal.{se "muscle strain." FUNCTIONAL ANATOMY OF THE MUSCLES OF THE CAT The muscles to be described have been organized into groups according to functional associavons and positional rela,tionships. For the most part, the organization closely follows the sequenre of dissection, Each group makes up a sort of functional system, and the student will avoid confusion 84 78 FUNCTIONAL ANATOMY OF THE MAMMAL in limiting himself, as far as possible, to the study of the muscles of one group at a time. Later, he should associate the functions of related groups and attempt to analyze the sequence of actions in performing a simple activity. A check list of the muscles in each functional group is given first to acquaint the student with the number of muscles and general character of each group. This is followed by a description of specific functional and structural features of the muscles comprising the group. The student may find it helpful to construct a table of muscles giving name, origin, insertion, action, and relationships as though the muscles acted separately,, which they do not do, however. Construction of such a table should be made from personal observations. For a more complete descriptive account of the muscles, Reighard and Jennings, "Anatomy of the Cat," should be consulted. The check list for each group includes the English application of the name; pronunciation is also given where thought to be helpful. In case no counterpart or homology for a muscle is present in man, the name appears in italics. The check list is numbered continuously through successive groups. THE EXTRINSIC MUSCLES OF THE THORACIC ApPENDAGE This system of muscles originates on the axial portions of the skeleton and inserts to the appendage in such a way as to hold the shoulder girdle in place and produce movement in the appendage mostly as a complete unit. Some, however, produce their principal action on the shoulder joint as will be seen from the insertions. Check list 1. Clavotrapezius (trap-e'ze-us). Clavicular portion of the trapezoid muscle in man. 2. Acromiotrapezius (ak-ro'me-o). Middle division of trape- \ zoid muscle inserting to the meta-acromion.,3. Spinotrapezius. Posterior portion of trapezoid muscle inserting to spine of scapula. 4. Latissimus dorsi (lat-is'im-us). Broadest muscle of the back. 5. Rhomboideus major (rom-boid'e-us). Rhomboid shaped between vertebral borders of scapulae. 6. Rhomboideus minor. Small rhomboid in man (largest of group in the cat). 7. Rhomboideus capitus. Rhomboid extending to head (same as occipitoscapularis). 8. Pecto-antibrachialis (pek-to-an-ti-bra-kea'lis). From breast to antibrachium. 85 A STUDY OF THE VOLUNTARY MUSCLES Pectoralis major (pek-to-ra'lis). Large breast muscle. 10. Pectoralis minor. Minor breast muscle. 11. Xiphihumeralis (ziph'e-hu-mer-a'lis). Xiphoid process to humerus. 12. Serratus anterior (serra'tus). Serrated muscle on the front. 13. Levator scapulae (le-va'tor scap'u-iae). Elevator of scapulae. 14. Levator scapulae ventralis (le-va'tor ven-tra'lis). Elevates scapulae from below. 15. Cleidomastoideus (kli'do-mas-toi'de-us). Clavicle to mastoid 'combined with a sternal division in man. as the sterno cleidomastoideus. Observations and dissection (see Fig. 4.5) Two groups of muscles are particularly concerned with holding the scapulae close to the vertebral column and pulling them together at the back to abduct the arms. These are the trapezius and rhom- FIG Comparison of superficial muscles in man and cat. boideus groups, and each has three divisions. The origin of the divisions of the trapezius extends from the supra-occipital bone of the skull back to ab'but the middle of the thorax. The c1avotrapezius passes over the side of the neck to insert to the rudimentary clavicle, which can be located by freeing the margins of the muscle. Since 86 80 FUNCTIONAL ANATOMY OF THE MAMMAL the clavicle is rudimentary in the cat, it is partly imbedded ill the muscle, and the clavotrapezius appears to continue over the front of the brachium. But this continuation of musculature from the clavicle to the forearm is the clavicular portion of the deltoideus, an intrinsic muscle 01 the appendage. The acromiotrapezius is readily identified by its dorsal aponeurosis over the vertebral borders of the scapula, and the spinotrapezius is a triangular division passing from the spinous processes of thoracic vertebrae to the spine'of the scapula. Each of the trapezius should be transected separately halfway between their origins and inser- Splenius Levator scapu loe Supraspi natus ~-""''=''- rlceps eres major erratus anterior Serratus posterior inferio FIG Second layer of thoracic muscles in man and cat. (Superfi cial muscles removed.) Note that the similarities in this layer arc greater bet ween the two forms than in the superficial layer. tions. Note especially the line of dissection in the spinotrapezius in which the dorsal fibers are very short and lie under the edge of the acromiotrapezius. Also take care in separating these two muscles. When the cut ends are pulled toward their attachments (reflected), the rhomboideus musculature is exposed, all of which inserts to the vertebral border of the scapula. Immediately behind and below the spinotrapezius is the large latissimus dorsi, which should be identified and transected. As previously mentioned, the rhomboideus major in the cat is relatively small and can be identified as the portion that overlaps the inferior angle of the scapula. The rhombpideus minor is quite extensive, and the more cranial fibers run diagonally from the spinous processes of the vertebrae back to the vertebral border of the scapula. The rhomboideus capitus (occipltoscapularis) is a thin ;:;trap-like ;:;lip extending over the neck to tb.e occipital bone. 87 A STUDY OF THE VOLUNTARY MUSCLES 81 In addition to abduction, the main mass of rhomboideus also draws the scapula craniad in a rotary manner. Opposing actions to the trapezius and rhomboideus are mostly performed by the breast muscles, the pectoralis group (Fig. 46). Here again the origin is extensive, from the manubrium to the xiphoid process of the sternum in the cat. The insertion to the humerus is designed not only for adduction, but also to keep the forearm held closely to the trunk by medial rotatipn. The most Coudo- Gluteus moximus Spino- } Acromio- deltoideus Clo vo- FIG The order of dissection, 1-5. Double lines indicate where tran:;ections are to be made. superficial of the pectoralis group is the pecto-antibrachialis, which partly covers the pectoralis major. Muscle fibers of the pectoantibrachialis and pectoralis major tend to run transversely across the breast, whereas the pectoralis minor, which merges with the major caudally, passes obliquely from more caudal sternebrae. The xiphihumeralis is the most caudal of the group, and its fibers extend even more obliquely to the humerus. It appears as a narrow strip from the xiphoid process and must be separated from the large latissimus dorsi and pectoralis minor in an arbitrary manner. The latissimus dorsi may now be transected and reflected if this has not already been done. The pecto-antibrachialis should be separated from the clavodeltoideus (continuation of clavotrapezius) at its cranial margin and both transected and reflected. This procedure exposes the broad insertion of the pectoralis major to the craniolateral margin of the humerus. The oblique fibers of the pectoralis minor should now be separated from the more transverse major fibers. Transection of the pectoralis major should be done carefully to avoid injury to underlying nerves to expose the. more limited insertion of the 88 82 FUNCTIONAL ANATOMY OF THE MAMMAL minor and xiphihumeralis. Attempt to follow the insertion of the latissimus dorsi to each side of the humerus, and note its relation to the insertion of the pectoralis muscles. Transect the medial insertion of the latissimus to expose the muscles on the front of the brachium. Transverse ju9ujar vein E",ternaf ju9ular --- vein.latissimus dorsi Rectus obdominis (beneath aponeu rosis) FIG Superficial muscles on the ventral aspect of the cat. A study of the attachments of the latissimus dorsi, from the dorsolumbar aponeurosis to the humerus, shows it to function in drawing the arm backward and dorsad. A thin extensiojl of the latissimus dorsi covers the medial aspect of the upper arm, as the epitrochlearis muscle. Since the pectoralis (except the pecto-antibrachialis) 89 A STUDY OF THE VOLUNTARY MUSCLES 83 insert to the craniolateral border of the humerus, they not only adduct the appendage, but also tend to rotate the humerus medially, which aids in pronating the hand. Observe the difficulty in your own body in drawing the arm in and supinating the hand simultaneously. The rhomboideus minor and major should be transected to free the vertebral border of the scapula from the vertebral column. This transection exposes a broad fan-shaped mass of muscles originating from the last nine or ten ribs and continuing its origin craniad to the lower borders of the last four cervical vertebrae. Actually, two muscles make up this sheet of musculature: the serratus anterior.arises from the ribs and the levator scapulre from cervical vertebrae; but no clear distinction can be made out between them where the fibers merge. The fibers of the serratus anterior pass to the more caudal part of the vertebral border of the scapula, whereas the levator scapula inserts mostly to the superior angle of the scapula. Observe that the body is suspended by these muscles with the appendages acting as supports for the suspension. Contraction of the levator scapula rotates the scapula forward and elevates it, which draws the arm backward. The serratus anterior acts in the opposite manner by depressing the scapula and rotating it backward to produce an upward thrust of the arm. If the two muscles on both sides contract simultaneously with the body suspended low between the vertebral borders, a springing action is performed, throwing the body upward with the appendages extended (see Figs and 4.11). Two other extrinsic muscles of the thoracic appendage are yet to be considered: the cleidomastoideus and levator scapulre ventralis. The latter is a strap-like muscle that merges with the acromiotrapezius on the scapula and passes obliquely across the neck under the clavotrapezius to the occipital bone of the skull. With the head in a fixed position, the muscle acts to draw the scapula dorsocraniad. The cleidomastoideus is closely associated at its insertion on the mastoid process with an intrinsic muscle of the axial skeleton, the sternomastoideus. The two form a triangular space where they diverge on the side of the neck, with the sternomastoideus passing to the sternum, the other to the clavicle. Note the external jugular vein passing between these two muscles and over the cleidomastoideus. The action of these muscles depends upon which attachment is to be stationary; usually the muscles function in turning the head and depressing it. 90 84 FUNCTIONAL ANATOMY OF THE MAMMAL Transections of the extrinsic muscles not yet cut may now be made after noting especially that nerves are not involved in the section. This leaves the appendage attached to the body by large nerve trunks and blood vessels. The nerves and vessels should be cleared of fascia to expose them and spare them from injury in further dissection. INTRINSIC MUSCLES OF THE THORACIC ApPENDAGE These muscles have both origin and insertion on appendicular bones and move parts of the appendage in relation to some other parts of the appendage. Muscles working principally over the shoulder joint With the exception of one (clavodeltoideus), these muscles all arise on the scapula and insert on the humerus and, therefore, function in moving the humerus at its articulation in the glenoid cavity of the scapula. Check list 16. Clavodeltoideus (del-toide'us). Portion of deltoid from clavicle. 17. Supraspinatus (spi-na'tus). Above the spine of the scapula. 18. Acromiodeltoideus (ak-ro'me-o). Portion of deltoid from acromion process. 19. Spinodeltoideus. Portion of deltoid from spine of scapula. 20. Infraspinatus. Within the infraspinatus fossa. 21. Teres major (te'res). Large round muscle. 22. Teres minor. Small round muscle. 23. Subscapularis (skap-u-la'ris). Beneath the scapula. 24. Coracobrachialis (kor'ak-o-bra-ke-a'lis). From coracoid process to brachium.. Observations and dissection As previously mentioned, the clavodeltoideus appears as an extension of the clavotrapezius; it arises from the insertion of the latter muscle and inserts to the antibrachial fascia in front of the elbow, on the ulnar side. The clavodeltoideus acts as an extensor of the humerus and flexor of the forearm in a forward stride of the appendage. Extension of the humerus is also effected by the supraspinatus, which lies under the acromiotrapezius and occupies the supraspinatus fossa. This muscle narrows to a tendinous sheath 91 A STUDY OF THE VOLUNTARY MUSCLES 85 passing over the front of the head of the humerus to the great tuberosity where it inserts. Two other divisions of the deltoids, the acromio- and spinodeltoideus, are named also from their points of origin, which roughly correspond with the insertions of the other trapezius divisions. These pass across to the deltoid ridge of the humerus to act as lateral rotators and abductors of the upper arm. Back of the spine of the scapula, and occupying the infraspinatus fossa, is the. infraspinatus muscle. The large teres major lies immediately adjacent, extending along the entire axillary border of the scapula. The infraspinatus passes to the lateral aspect of the head of the humerus, whereas the teres major runs to the medial aspect to insert to the lesser tuberosity. of the humerus. Although both may act as flexors of the humerus, the insertion of the teres major indicates it to be also a medial rotator of the humerus, and the infraspinatus a lateral rotator. Simultane!Jus action of the two would appear to draw the humerus directly backward. The teres minor is a small round muscle which is exposed by transecting and reflecting the spino- and acromio-deltoideus, under which it lies. The teres minor arises from the distal third of the axillary border of the scapula, and its insertion can be easily separated from that of the infraspinatus on the greater tuberosity. It apparently aids in flexion and lateral rotation of the humerus. This group includes two other muscles, which occupy the medial aspect of the appendage: the subscapularis and coracobrachialis. The subscapularis occupies the subscapular fossa of the scapula between the supraspinatus in front and the teres major behind. Its fibers converge into a tendon that crosses the shoulder joint to insert to the lesser tuberosity. The muscle aids in holding the joint in place and in drawing the humerus mediad. The coracobrachialis is a tiny muscle running from the coracoid process to the humerus and is variable as to its exact point of insertion. It appears to serve more as a ligament in keeping the joint tensed in adduction. Muscles of the upper arm These muscles act principally over the elbow joint, mostly to produce extension and flexion of the forearm. But the actions of some are complicated, as will be seen in tracing their origins and insertions. Check list Muscles of the btachium (flexors and extensor of elbow joint). 25. Epitrochlearis (ep-e-trok'le-a-ris). From above the trochlea; occasionally a part is anomalous in man. 92 86 FUNCTIONAL ANATOMY OF THE MAMMAL 26. Triceps brachii. Three-headed muscle of brachium; additional parts in the cat. 27. Anconeus (an-ko'ne-us). Pertaining to the elbow. 28. Brachialis anticus (bra-kea'lis an-ti'kus). Against the brachium. 29. Biceps brachii (bra'chii). Two-headed muscle of brachium; one head in cat. ~ Observations and dissection In the cat, a thin wide extension from the latissimus dorsi covers the medial aspect of the brachium. This is the epitrochlearis, which serves to help hold the humerus adducted. It should be transected and reflected. The extensors of the forearm are mostly located on the back of the humerus, and all insert to the olecranon process of the ulna. The action is produced by the triceps brachii and anconeus. In quadrupeds, these are especially well developed since a considerable portion of the body weight is supported by the extended forearm. Instead of three divisions of triceps as in man, additional slips of this muscle occur in the cat. Superficially on the back of the arm the long head of the triceps extends from the glenoid margin of the scapula to the olecranon, thus passing over both the shoulder and elbow joints. The broad lateral head of the triceps lies immediately in front of the long head on the lateral aspect of the arm. These two heads should be well separated, transected, and reflected to expose the endotriceps, which consists of three slips in the cat. Note that the lateral and endotriceps originate on the \ humerus. The anconeus extends from. the external epicondyle of. the humerus to the olecranon process of the ulna, forming a triangular area of rather short muscle fibers. Flexion of the elbow is produced by two muscles: the biceps brachii and the brachialis anticus. The biceps brachii is mostly covered in quadrupeds by the overlying pectoralis musculature. It occupies the cranial aspect of the humerus and extends from the glenoid border of the scapula to the bicipital tubercle of the radius. The tendon of origin is rather unique in that it passes through the capsular ligament of the shoulder joint and aids in holding the head of the humerus into the glenoid fossa of the scapula. The brachialis anticus superficially appears to be an extension of the acromiodeltoideus, but is a different muscle entirely. It originates at the deltoid ridge and lateral aspect of. the humerus and inserts on the coronoid process of the ulna immediately below the elbow joint. Note that the two flexors are entirely distinct in 93 A STUDY OF. THE VOLUNTARY MUSCLES 87 origins and insertions. The biceps brachii is not a powerful flexor with the hand pronated. It is a supinator of the pronated hand when the arm is flexed and the hand pronated. Observe particularly the state of contraction in your own biceps brachii in performing Extensor carpi radialis lon9us and brevis' Extensor carpi ulnaris 'flexor carpi ulna ris ~-1IIM' -- Extensor diqitorul11 co m m u n is ~ Ixtensor diqitorum latera I is FIG Lateral muscles of the thoracic appendage of the cat. triceps has been reflected.) (The lateral head of the flexion with the hand in the different positions of flexion and pronation. Note the shift in position of the bicipital tubercle of the radius under these circuillstances on an articulated skeleton. Only the short head of the biceps brachii of man is represented in ~he cat. 94 88 FUNCTIONAL ANATOMY OF THE MAMMAL MUSCLES OF THE FOREARM Most of the muscles of the forearm are concerned with movement at the wrist and within the hand, but some rotate the radius in producing pronation and supination. Extensors of the wrist and digits occupy the back of the forearm and are associated with supinators, whereas the flexors are located on the opp osite side (palmar surface) and are associated with pronators. Observe the relative difficulty in flexing the digits simultaneously with supinating the hand and how extension and supination of the hand are easily performed simultaneously. Only by carefully following the tendons of insertion in these muscles is it possible to determine whether the action is on the carpal bones (wrist) or on the phalanges (digits). A careful dissection of this group of muscles is necessary to a proper understanding of coordinated movements and activities of the hand. In most instances the names of the muscles are descriptive of their position and particular action, and they should be identified mostly from the names. Extensors and supinators Check list 30. Brachioradialis (bra'ke-o radia'lis). Brachium to radial side. 31. Extensor carpi radialis longus (car'pe). Long extensor of wrist from radial side. 32. Extensor carpi radialis brevis (bre'vis). Short extensor of wrist from radial side. 33. Extensor digitorum communis (kom-u'nis). Common extensor of digits. 34. Extensor digitorum lateralis (lat-er-al'is). Extensor of digits on midlateral aspect (extensor digiti quinti proprius in man). 35. Extensor carpi ulnaris (ul-na'ris). Extends the wrist from ulnar side. 36. Extensor pollicis brevis (pol'lic-is). Short extensor of thumb. 37. Supinator (su-pin-a'tor). Supinates hand. 38. Extensor indicis. Extends index finger. Begin the dissection by carefully removing the tough sheath of aponeurotic fascia that binds the muscles together and tends to enclose them. On the cranial border and radial aspect of the forearm, this fascia is closely bound to an extreipely slender muscle accompanied by a rather conspicuous nerve, both of which terminate superficially at the hand. The muscle is the brachioradialis, 95 A STUDY OF THE VOLUNTARY MUSCLES 89 which originates on the humerus and spirals over the brachialis anticus to reach the craniomedial aspect of the lower arm and hand. The nerve is the radial branch of the musculospiral nerve, which lies under the lateral head of the triceps brachii muscle. A void injury to both. Using the brachioradialis, a supinator, as a landmark, five superficial extensors are seen from the radial to the ulnar side. These are, in order, extensor carpi radialis longus and brevis, extensor digitorum communis, extensor digitorum lateralis, and extensor carpi ulnaris. These all arise from the lateral supracondylar region of the humerus and insert either to the metacarpals or carpals (carpi) or to the phalanges (digiti), as the names indicate. The tendons of the muscles that reach the fingers pass through transverse ligamentous tissue at the wrist, some of which should be left intact to hold the tendons in their proper positions, while the tendons on the back of the hand are exposed. To demonstrate the actions of the digital muscles, all the extensors should be transected at slightly different levels, and by pulling on the insertion tendons, the muscles to which they belong may be identified. Usually the extensor digitorum lateralis inserts to the middle, fourth, and fifth digits, and its tendons lie beneath those of the communis. Flex the digits sharply, then pull on the insertion end of these muscles to demonstrate their actions. By following down the course of the extensor carpi radialis and brevis to their insertions to the second and third metacarpal bones, their tendons are seen to pass under a diagonal mass of musole that tapers to a narrow tendon inserting to the thumb and index finger. This overlying muscle is the extensor pollicis brevis, which has a broad origin on the shaft of the ulna and must be transected to follow the insertion tendons of the extensor carpi radialis. A special extensor of the index finger, extensor indicis, lies under the transected extensor carpi ulnaris. I ts tendon runs from the origin on the ulna diagonally across the forearm as a narrow strip to insert to the base of the second phalanx of the index finger. At the wrist, it is held in place by the transverse ligaments over the carpal bones. It is interesting to note that the extensors pollicis and indices have their origins on the relatively fixed ulna and must cross the radius in reaching their points of insertion on the thumb side of the hand. This prevents the muscles being stretched, as they would be, if they arose from the radius, when the radius rotated in supinating the hand. 96 90 FUNCTIONAL ANATOMY OF THE MAMMAL The supinator lies directly above the origin of the pollicis brevis and may appear continuous with it overlying the radius. It arises from tendinous connections from the elbow joint and ulna to wrap itself partly around the radius so as to rotate it laterally in producing supination of the hand. In man, the supinator and brachioradialis are the special supinators of the hand, and their homologues in the cat are obvious, but not so well developed. The extensor digitorum lateralis is represented by the extensor digiti quinti proprius in man, and the extensor pollicis brevis of the cat is represented in man as two muscles, extensor pollicis longus and brevis. Abductors and adductors of the thumb are highly developed in man also and mostly missing in the cat. Obviously, the hand of man is more complex than that of the cat, particularly with reference to the use of the digits and the thumb in opposition to the other fingers. Flexors and pronators As previously mentioned, the ventral or palmar aspect of the forearm is occupied by flexors of the wrist, flexors of the digits, and special pronators of the hand. The wrist is capable of being overextended with the hand bent upward, a condition that has been called dorsiflexion, but that should not be confused with flexion as described here. Observe on yourself the difficulty in flexing the digits while the wrist is also sharply flexed. Pull the skin tightly across the wrist, and observe the appearance of a broad band running transversely across the area above the wrist on its palmar surface. This band is produced by the presence of transverse ligamentous tissue that \serves to hold the cord-like tendons in their proper places. Flex the digits strongly, and attempt to locate the position of the muscles on the forearm which are producing the actions. Determine which digits tend to operate most independently, and observe that the tendon to the index finger crosses from the ulnar to the radial side. In man, two conspicuous tendons will usually be seen above the wrist: one lies in the middle of the area, and the other lies to the radial, or thumb, side. The middle tendon belongs to the palmaris longus muscle and the other to the flexor carpi radialis. An interesting circumstance occurs in man with respect to the palmaris longus. In about 10 per cent of cases, the muscle is entirely lacking. In one exceptional circumstance, three students in a class of 15 showed no evidence of possessing a palmaris longus. This is such a common condition that it is considered as a variation and not as an 97 A STUDY OF THE VOLUNTARY MUSCLES 91 anomaly. It has not been reported as being missing in the cat even as an anomaly. Triceps 6rachii ;~-Epitrochlearis process Clavodelt-oideus Pectoantibrachalis.:~~~ Biceps 6rachii ---"' Brach iarad ia I is --_ Pronator teres Flexorcarpi ulnoris Il... ~\t-- humera I head and 11I 111I1I1111I.m_-u Ina r head Extensor carpi radio lis \oll9 us -1\"1' and brevis ----+H 11I1I 11I1 ~--'#4,II--.3 rd h ea d of Flexor' profundus diqitorum and r/~flfl-th--- 5th he a d FIG Muscles on the medial aspect of t lw antibrachium. Check list 39. Palmaris longus (pal-ma'ris). Long muscle on palmar surface. 40. Flexor digitorum sublimis (sub-li'mis). Delicate flexor of the digits. 41. Flexor digitorum profundus. Deep flexor of digits. 42. Flexor carpi ulnaris (car'pi). Flexor of wrist from ulnar side. 43. Flexor carpi radialis. Flexor of carpi from radial side. 44. Pronator teres (te'rez). A round pronator; term not descriptive for cat., 45. Pronator quadratus (kwad-ra'tus). Quadrate-shaped pronator. 98 92 FUNCTIONAL ANATOMY OF THE MAMMAL Three muscles of this group are flexors of the digits and hand: palmaris longus, flexor digitorum sublimis, and flexor digitorum profundus. The palmaris longus serves as a landmark. It is the broadest superficial muscle on the ventral surface and arises from the medial epicondyle of the humerus. Its insertion is complicated. After transecting it, follow the insertion end toward the wrist through the transverse ligament and note that two divisions are formed. A fleshy ulnar division extends from the outer border of the tendon to become a portion of the flexor digitorum sublimis. The flat tendinous division diverges into the palmar fascia as four or five tendons. Most of the tendons send a branch to the heavy trilobed pad in the palm. The main tendons insert to the first phalangeal bones to flex the hand. Carefully dissect across the next deeper layer of ligamentous tissue, and probe deeply within the wrist region to expose the extremely heavy tendon of the flexor digitorum profundus. A second portion of th~ flexor digitorum sublimis arises from this muscle and is located as a small mass on the superficial aspect of the profundus tendon and can be separated easily from it. Now trace the delicate tendons of the parts of the flexor digitorum sublimis to their attachments; note how they are perforated to allow tendons of the profundus to pass through. If time permits, locate fibrous, pulley rings at the bases of the first phalanx of the digits, which keep. the tendons in place. The flexor digitorum profundus possesses five heads which converge to the common tendon, which, in turn, redivides into five \ tendinous parts, one for each of the digits. The insertions are to \the terminal phalanges. Before attempting to identify the heads of the flexor profundus, the flexors of the wrist should first be studied and transected. On the ulnar side, the two conspicuous heads of the flexor carpi ulnaris should be observed. An ulnar head of this flexor arises from the surface of the olecranon process of the ulna; the other head is from the medial epicondyle of the humerus in connection with the flexor profundus (second head). The ulnar nerve passes between the two heads of the flexor carpi ulnaris. The two heads join into a common tendon to insert to the pisiform bone of the wrist. On the radial side, only one muscle inserts to the wrist region, the flexor carpi radialis. This slender muscle originates from the medial epicondyle of the humerus and inserts :m the base of the. second and third metacarpals. 99 A STUDY OF THE VOLUNTARY MUSCLES 93 The flexors of the wrist should now be transected and the separate heads of the flexor digitorum profundus traced from the common tendon to their positions of origin. The first head is from the ulna on its radial border; the second, third, and fourth heads are from the medial epicondyle of the humerus; the fifth head is from the interosseous membrane between the radius and ulna and from the periosteum of these bones. Epitrochrearis "Pectora lis M, Biceps brachi i N, Musculo-cutaneOu5 FIG Muscles on the medial aspect ot the r'ight thoracic appendage with reference to the brachial nerve plexus. The short and long anterior thoracic nerves to the pectoralis musculature are not shown. The extrinsic muscles have all been transected and the appendage turned away from the body. Return appendage to normal position to determine relationships. The two pronators are now left to be identified. The pronator teres is a relatively short muscle extending diagonally from the medial epicondylar area of the humerus to the medial aspect of the proximal half of the radius. The action is medial rotation of the radius to produce pronation. The pronator quadratus lies deep beneath the tendon of the profundus as a mass of short muscle fibers ~ that run obliquely from the ulna to the radius to function like the pronator teres (see Fig. 2.25). 100 94 FUNCTIONAL ANATOMY OF THE MAMMAL The innervation of the muscles thus far studied can now be determined. This is described on page 197, and illustrated in Fig PRINCIPAL IVluSCLES OF RESPIRATION The intrinsic muscles of the thorax are those which have both origin and insertion on the thoracic skeleton and are mostly concerned with respiration. By respiration, in this connection, we refer to respiratory movements, or breathing which keeps the lungs ventilated. The thorax acts as a bellows: when it is increased in size, air rushes in; when it is decreased, the air is forced out. Muscles of respiration furnish the power that operates the bellows; the ribs are the levers. The thoracic vertebrae and sternum are the more fixed parts of the thorax and of the respiratory bellows. The floor of the thorax is formed by one of the principal respiratory muscles, the diaphragm, which will be studied later when the body cavity is opened. Note that on inspiration the ribs are elevated; on expiration, they are depressed. Check list 46. Diaphragm. (To be observed later.) 47. Serratus posterior superior. Serrate muscle on back toward head; named with reference to human posture. 48. Serratus posterior inferior. Serrate muscle on back a~d posterior. 49. External intercostals. Between ribs on outside. 50. Internal intercostals. Between ribs but deeper. 51. Scalenus (ska-ie'nus). Unequally three-sided. 52. Levatores costarum (le-va-tor'ez). Elevators of ribs. Dissection and observations First observe that some of the musculature of the thoracic wall passes only from one rib to an adjacent rib and that other musculature passes over ribs when traced from one attachment to the other. Two serrated muscles lie on the dorsolateral aspect of the thorax, the serratus posterior superior and inferior. The first originates in a thin aponeurosis extending from the cervical region to about the tenth rib. The muscular serrations extend ventrocaudad to insert to the ribs. The serratus posterior inferior lies just caudad to the superior and may be distinguished from it by the serrations, which here are directed ventrally to the last four or fiv~ ribs. The action 101 A STUDY OF THE VOLUNTARY MUSCLES 95 of both is in pulling the ribs craniad in inspiratory movements. These may be transected to determine their relationships. By locating an area where the bony portions of the ribs are clearly shown, muscle fibers will be seen to occupy the intercostal spaces. The external intercostals are superficial, and the fibers are directed ventrocaudad, connecting adjacent ribs only. By carefully transecting these fibers, a second layer will be seen to underlie them. This layer consists of the internal intercostals, which are directed opposite to the externals. Contraction of external intercostals produces inspiration, whereas the internals act in expiration. The thin membrane lining the internal intercostal muscles is the parietal pleura. The main trunks of the nerves of the brachial plexus pass between divisions of scalenus musculature on the thorax and neck. Three prominent divisions of the muscle occur together with variable slips. A dorsal division extends back to the third rib, a medial division to the seventh or eighth ribs; these join with a cervical porti8n to attach on the transverse processes of cervical vertebrae... Scapula FIG Diagrammatic representation of muscles that hold the thoracic appendage to the axial skeleton. ' The scalenus acts to draw the ribs craniad when the neck is fixed or to bend the neck when the ribs serve as the origin. Immediately below the scalenus is a thin muscle passing from the first rib to the sternum. This is the transverse costarum, which functions to pull the sternum craniad. The levatores costarum are continuous with external intercostals dorsally but lie deep under a heavy muscle of tbe thoracic vertebrae (longis:;imus dorsi). The 102 96 FUNCTIONAL ANATOMY OF THE MAMMAL levatores are small muscles running from transverse processes of thoracic vertebrae to the angle of the rib below. They function with the external intercostals in inspiratory movements. It will be noted that inspiration requires considerable active energy and that expiration is relatively passive. Thoracic region of trun~ / /..._------,..,/, - --contracted appendicular bones extended beneath body. FIG Diagram to show how the serratus anterior helps support the body of a quadruped. Broken lines indicate its possible action in springing the body upward. AXIAL MUSCLES OF THE NECK These muscles have both their origins and insertions on axial parts of the skeleton and except for the sternomastoideus lie beneath the extrinsic muscles of the thoracic appendages. They produce movement of the head and neck. Check list 53. Splet;tius (sple'ne-us). A compactly bound muscle. 54. Longissimus dorsi. Longest muscle on dorsal aspect. 55. Sternomastoideus. From mastoid to sternum. 56. Sternohyoid. From sternum to hyoid. 57. Sternothyroid. From sternum to thyroid ~artilage. 58. Thyrohyoid. From thyroid cartilage to hyoid bones. 103 A STUDY OF THE VOLUN1'ARY MUSCLES 97 Identification and dissection The splenius is a large thick sheet of rrluscle (one on either side of the neck) lying beneath the trapeziu~ group and rhomboideus capitus. It originates from the nuch~ (neck) ligament, which occupies the middorsal line of the neck, and from deep fascia; the insertion is to the lambdoidal ridge of the skull. The two together raise the head. When they act separately, the neck is bent latetally right or left. Caudally, the splenius is closely associated with the thick longissimus dorsi musculature, which fills the area between the spinous processes of the last two or three cervical vertebrae and extends caudally along all thoracic and lumbar vertebrae. On the ventral aspect of the neck, the stemomastoideus passes from the lambdoidal ridge and mastoid process to the manubrium. 'Ibis bas been aescribea in connection' wlt'h the c'ieloomasto"hleus with which it functions in turning the head. The inner surface of the sternomastoideus is in contact with a slender muscle, the sternohyoideus, occupying the mid-ventral lioe of the neck and named also from its origin and insertion. It acts' to draw the hyoid bone caudad. The sternothyroid is directly beneath the sternohyoid but extends only from the first costal ca:(tilage to the thyroid cartilage of the larynx, which it draws back. These muscles should be divided in the midline of the neck by blunt dissection, to expose the trachea, :;LS far as the manubrium of the sternum. CHIEF MUSCLES OF MA-STICATION These muscles lie under the thin superficial muscles of facial expression, which will not be described here. Of the six principal muscles of mastication, five are elevatore of the lower jaw and but. one, the last on the check list, is a depre;3sor. Check list 59. Masseter (mas-e'ter). A chewer. 60. Temporal. Pertaining to position in temporal fossa. 61. Pterygoideus externus (ter-ig-oid'e-us). Wing-shaped on outside. 62. Pterygoideus internus. Wing-shaped on inner side. 63. Digastric. Two-bellied muscle. Identification and dissection J The location of two of the most powe:fful muscles of mastication should first be determined on yourself by pressing firmly on the 104 98 FUNCTIONAL ANATOMY OF THE MAMMAL side of the jaw and closing the jaws strongly. The prominent muscle felt to contract is the masseter, which in the cat arises in three layers from the malar bone and zygoma to insert to the coronoid process and lateral fossa of the mandible. Now press the fingers to the temporal fossa, just back of the posterior rim of the orbit, and close the jaws firmly to feel the contraction of the temporal muscle. The. temporal arises in the temporal fossa and passes to both surfaces of the coronoid process of the mandible. These are powerful muscles used in biting. Other muscles of mastication should not be dissected until the salivary glands are studied. The pterygoideus externus lies on the medial aspect of the mandible just below the lower portion of the temporal. It arises from the pterygoid process and vertical sheet of palatine bone which projects caudad from the horizontal portion of palatine. The pterygoideus internus is connected to the externus caudally. It arises in the fossa of the pterygoid process and inserts with the externus and its tendon to the medial surface of the angle of the mandible. The pterygoideus externus and internus also assist in closing the jaw. As is commonly known, the mouth drops open upon relaxation of the elevators of the jaw. The most active muscle in forcefully opening the mouth (depressing the jaw) is the digastric. This muscle lies mediad to the angle of the jaw where it is inserted. Its origin is from the outer surface of the skull near the jugular and mastoid processes. In the cat, its two parts are not so prominent as in man, one part being thick and fleshy from the jugular process, the other a thin tendon from the mastoid process which then broadens out to the insertion. The insertion is to the lower border of the mandible at the level of the molar tooth. The lever arm is fairly long but not especially efficient, and it is much easier to hold an. animal's jaws together than to pull them apart. :MUSCLES OF THE ABDOMINAL WALL These muscles cover the dorsolateral and ventral aspects of the abdomen. Some of them extend craniad over a considerable area of the thorax. Because of the thoracic connections, the group is sometimes considered together with the muscles of respiration as the thoracoabdominal muscles. The active function of the abdominal muscles is in producing constriction and cpmpression of the abdomen. Normal tonus in the musculature aids in supporting the viscera in the proper position. Constriction of the abdomen 105 A STUDY OF THE VOLUNTARY MUSCLES 99 forces the viscera principally upward and causes the diaphragm to elevate in forceful expirations. This expiratory action is also aided by a downward pull on the sternum and ribs. Note a tightening of the abdominal musculature in coughing. Active constriction of the abdominal muscles occurs in defecation and in the process of giving birth (parturition). Three of the group of four muscles occur as thin layers, or sheets, closely applied together on the lateral aspect, and the fourth extends along the longitudinal axis of the front of the abdomen. Check list 64. External oblique. Passing obliquely on the outside. 65. Internal oblique. Passing obliquely but deeper. 66. Transversus abdominis. Fibers run transversely over abdomen. 67. Rectus abdominis. Straight muscle of abdomen. Identification and dissection The external oblique is by far the most extensive of the group. It attaches cranially at the digitations of the serratus anterior and extends caudally to the junction of the body wall with the leg. Dorsally, the external oblique arises from the dorsolumbar aponeurosis. The insertion of the two sides is at the mid-ventral line (linea alba) by means of wide aponeurotic sheaths. These longitudinal sheaths enclose the rectus abdominis. In man, the junction of the external oblique with the leg is characterized by the presence of a thickened connective-tissue attachment, the inguinal ligament. This specialization is not obvious in the cat. Observe that the lower part of the inguinal region is not covered by muscle fibers of the external oblique, but only by a thin aponeurotic extension of it. Locate the most cranial portion of the external oblique, and observe that the fibers here are relatively short but are directed caudoventrad as they are further caudad. Mark out a line of incision to transect the muscle craniad to caudad. Make a shallow cut, and reflect the fibers to determine their depth. A second layer, the internal oblique, will be recognized by the fibers here running in an opposite direction. Transect and reflect the entire external oblique to expose the extent of the int~rnal oblique and the rectus abdominis. The rectus is attached cranially to the sternum and first and second costal cartilages. I t passes to the ischiopubic. symphysis; the 106 100 FUNCTIONAL ANATOMY OF THE MAMMAL abdominal portion of the rectus is rather completely surrounded by aponeurotic sheaths of the obliques. Note interruptions by transverse tendinous inscriptions along the rectus abdominis. In man, these interruptions produce a corrugated appearance of the mid-ventral aspect of the abdomen when it is strongly compressed. The internal oblique is neither so extensive nor so thick as the external. Transection of its fibers reveals the fibers of the transversus, which is also relatively thin and limited in extent. It can be identified by the more transverse direction of its fibers and also by the parietal peritoneum lining the abdominal wall, which is applied to its inner surface. Reexamine the character of the abdominal wall in the inguinal region. Here the wall is particularly weak, and in man the intestine may be forced through to enter the inguinal canal in the male,, or to push under the skin at the outer lip of the vagina in the female. This condition of rupture is known as inguinal hernia and is much more common in the male as the most usual type of rupture. Inguinal hernia in girl babies sometimes occurs as a result of extreme compression on the abdomen while they are being delivered through the birth canal of the mother. The anatomy of these potential conditions will be better observed when the abdominal cavity has been opened.. MUSCLES OF THE PELVIC ApPENDAGE The muscles that originate on the pelvis are of two rather distinct types: (1) those which have an immediate insertion on the. femur and (2) those which pass over both the hip and knee joints to insert on the shank at the tibia or fibula. In addition to these types is a third group that affects the hip joint, consisting of powerfulloin muscles. These originate mostly along the lumbar vertebrae and insert to the femur and girdle. This latter group functions especially in bending the back down on the legs when the legs are fixed, as in stooping, and some act in flexing the femur when the back is fixed, as in sitting erect and drawing the thighs toward the abdomen. Because of their position, the loin muscles are best studied in connection with internal anatomy and are described with reference to the sacral and lumbar nerve plexi (page 200). Actions of the pelvic appendages are described as though the legs were not supporting the body weight and were free to move in all possible directions. Actions at the hip joint are similar in type to those at the shoulder, but are more restricted in range. For example, the femur cannot 107 A STUDY OF THE VOLUNTARY MUSCLES 101 be rotated as freely as the humerus, nor can it be abducted or extended in so great a degree. The bony landmarks of the appendage should be reviewed. Note particularly the position of the crest of the ilium, the great trochanter of the femur, the ischial tuberosity, the crest of the tibia, the external malleolus of the fibula, and the calcaneum. Oriqin ~-~JUI--Aponeurosis of Tensor foscia 10+0 over Gluteus medius <Ii-.lfll--.JI...-Muscu la r porhon._; :~i~\\'tii:lr'rlrln'i'~f~lf"frrr'rmj <;>t T. {~"'I:. ' c. \t>1tl and its ~-:J.IW,.~J-Insertion aponeurosis over Quadriceps femoris Course of Sci nerve beneoth1l1lr-t-...;_-.! the Biceps femoris ~,._.. FIG The distribution of aponeuroses on the lateral aspect of the pelvic appendage and the order of the muscle transections, 1-5. Preliminary dissection and identification Observe first a tough aponeurotic sheath on the craniolateral aspect of the thigh. This is the tendinous insertion of the tensor fascia lata muscle,,md it should not be broken into. Immediately in front of the fascia lata is the sartorius muscle which covers the 108 102 FUNCTIONAL ANATOMY OF THE MAMMAL cranial aspect of the thigh and extends medially as far as the femoral artery and vein. Directly back of the fascia lata is the thick and broad biceps femoris, while the gracilis superficially covers the Gluteus l1'laximus ~... +-Rectu.s femoris ~\!I.I~~':---":':""""':'I-- Tenuissimu s (cut) Sem.itendi.nOSlJ s Adductor femoris -+--'ft Adductor lon9us -T-:-'\t';--~!Q1 Semimembranosus -T-+~ Go strocnem ius llotero I h eo d) Insertion of B ice ps femoris "+I:::.:n"---txtensor lonqus di'litorum ftl/iff'7'f;-~--peroneus tertius FIG Muscles seen on the lateral aspect of the Ilelvic appendage with superficial muscles transected. Aponeurotic Jascia has been mostly removed hom the gluteus medius. caudomedial aspect of the thigh not cc)vered by the sartorius. The exact limits of these muscles should be determined and transections made of the sartorius and gracilis. Obtserve a he'c1vy mass of musculature passing from the ischiopubic symphysis diagonally down 109 A STUDY OF THE VOLUNTARY MUSCLES 103 to insert directly to the femur. This is mostly adductor femoris, which is divisible in the cat as slips rather than as distinct and separate adductors. The adductor portions should be distinguished from "hamstring" muscles passing across the back of the joint to the tibia. Returning now to the tensor fascia lata, observe that it originates from a fleshy extension occupying the area on the undersurface of the ilium and from tough aponeurotic tissue over the upper rump region. Its muscle fibers make up only a short irregular part of the muscle as a whole. The tough aponeurotic tissue over the musculature of the rump must be largely sacrificed in identification of the muscles. The largest of the buttock muscles of the cat is the gluteus medius, which originates on the lateral aspect and crest of the ilium and inserts to the great trochanter. The gluteus minimus lies directly beneath and medial to its lateral margin. Back of the medius is the gluteus maximus, a small triangular muscle in the cat, the cranial portion of which merges closely with tensor fascia lata fibers. The minimus and medius are principally extensors and rotators of the femur, while the maximus of the cat appears to be mostly an abductor. The caudofemoralis can now be identified directly behind the gluteus maximus and between it and the biceps femoris with which it inserts. These should be separated and transected. Care should be taken to avoid cutting the large sciatic nerve, which lies directly beneath the biceps femoris. Check list Principal muscles working only over the hip joint (muscles 73 to 77 to be dissected later). 68. Gluteus medius (glu-te'us). Middle buttocks muscle. 69. Gluteus maximus. Largest buttock muscle (small in cat). 70. Gluteus minimus. Smallest buttocks. 71. Caudofemoralis. From tail to femur. 72. Adductor femoris (See also adductor longus and brevis, Fig. 4.14). Adductors of femur. 73. Psoas major (so'as). Major loin muscle (see page 200). 74. Psoas minor. Minor loin muscle (see page 200). 75. Iliopsoas. Loin to ilium (see page 200). 76. Pyriformis (pir-if-or'mis). A pear-shaped muscle. 77. Gamelli (jem-el'e). Pertaining to twins (superior and inferior). 110 104 FUNCTIONAL ANATOMY OF THE MAMMAL The muscles that pass over both hip and knee joints have been described by some as producing actions at both joints. But we may consider their principal function as acting on the knee joint rather than at the hip, because these actions can occur regardless of the position of the femur. Check list 78. Sartorius. Tailor muscle (from cross-legged position). 79. Tensor fascia lata. A tensor of lateral fascia. 80. Biceps femoris. Two-headed muscle of femur. 81. Gracilis (gras/ii-is). From slender condition in man. 82. 'Semitendinosus. Name not applicable for cat. 83. Semimembranosus. Name not applicable for cat. Quadriceps femoris. Four-headed muscle of the thigh [only the rectus femoris (86) passes over the hip joint]. The four parts of the quadriceps femoris are: 84. Vastus lateralis. Large muscle on lateral aspect. 85. Vastus medialis. Large muscle on medial aspect. 86. Rectus femoris. Straight along the femur. 87. Vastus intermedius. Large intermedial muscle. Further identification. The extensors of the knee joint pass principally to the patella and occupy the front of the thigh and are enclosed by the sheath of the tensor,fascia lata, which is bound to their insertion tendons. The muscles are collectively known as the quadriceps femoris. Carefully and completely transect the muscular part of the tensor fascia lata and peel the distal insertion half down to the knee. It is seen to envelop a large muscle on the craniolateral aspect, the vastus lateralis, and an extensive muscle on the medial aspect, the vastus medialis. The margins of these muscles meet at the cranial aspect of the thigh a~d when separated reveal a strong round muscle invested between them. This is the rectus femoris, which should be transected and reflected to expose its positions of origin and insertion. Under the rectus femoris and originating directly on the front of the femur is the fourth part of the quadriceps, the vastus internus. Of the four quadriceps, only the rectus femoris originates on the pelvis. This muscle originates on the ventral border of the ileum so that it could conceivably serve to flex the femur and extend the tibia when these actions occur simultaneously as in kicking a football. The other quadriceps originate along the femur, and all make final attachments from the patellar area to the' front of the tibia just below the knee. The patella serves not only in protecting the knee 111 A STUDY OF THE VOLUNTARY MUSCLES 105 joint from injury, but is highly specialized to afford more efficient leverage in extending the tibia. With your knee joint fully extended and the leg muscles fully relaxed, observe that the patella moves freely from side to side when pushed with the fingers. But when the extensor muscles are tightened (contracted), ~:~\'\\;~,..-Vostus laterolis ~~~~-Adductor brevis.~~t-rectus femoris Adductor femoris Semimembranosus Adductor lon9us -"""t\'~"""~~ Semitendinosus Insertion of Sartorius Gastronemius (medial head)-~-' Insertion of Gracilis Popl iteu s --t------:fi::9:~ "flexor longus d i 9 i to ru m --+'''r---'--:?-a~ flexor lon<jus hallicus t.f"--nfo''i', Sol e u s ---+i~"1 1/ Tendon of pia Fro Muscles on the medial aspect of the P'llvic appendage, and semitendinosus have been removed. Portions of the gracilis the patella may be felt to be pulled and becomes immobilized as to movements in side directions. This fixation Qf the patella occurs regardless of the position of the femur (extended or flexed). The patella is formed in the tendon of the rec ~u s femoris as a sesamoid type of bone. Flexion at the knee is accomplished by three principal muscles : the biceps femoris, previously observed, th(~ semitendinosus, and the semi- 112 106 FUNCTIONAL ANATOMY OF THE MAMMAL _, membranosus. The tendons of these muscles are commonly known as the hamstrings. By pressing with the fingers on the medial aspect of the back of the knee in man, two tendons can be felt distinctly and one on the lateral aspect. The concavity between is the popliteal space. The lateral tendon is that of the biceps femoris; the heavy more medial of the other two is the semimembranosus; the more superficial is the semitendinosus. In the cat, the biceps femoris arises as a narrow portion from the ischial tuberosity. Its insertion has been noted as a broad aponeurotic sheath over the lateral aspect of the shank. Both semitendinosus and semimembranosus arise on the lower portion of the ischium. The semimembranosus is the more fleshy of the two and inserts immediately below the adductor femoris and may appear to be continuous with it. The insertion tendon of the semitendinosus is slender and the point of attachment on the tibia considerably lower than that of the semimembranosus. Some authorities consider the semimembranosus to consist of two parts, the upper part, which inserts to the femur and acts as an extensor and adductor of the femur, and a lower division inserting below the knee joint. In the present interpretation, the so-called upper portion has been regarded as being more nearly related to the adductor femoris than to the hamstring muscles and is called the adductor longus. The adductor brevis lies above the adductor femoris. The medial hamstrings pass to the medial aspect of the tibia to reach the crest, while the biceps pulls from the lateral aspect. This condition of insertion helps prevent a rotating strain on the hinge-type knee joint.. MUSCLES OF THE SHANK These muscles are similar in general character to the muscles of the forearm, but are neither so numerous nor so complex as arm muscles, since actions at the ankle and foot are more restricted than those of the wrist and hand. Care should be taken in tracing the tendons of the muscles reaching the more distal tarsals, metatarsals, and phalanges. These tendons are held in place at the ankle by crura1ligaments that must be broken through in following insertions. The muscles should be carefully separated and traced well to origins and insertions. Check list 88. Gastrocnemius (gas-trok-ne'me-us). Belly-like leg muscle. 89. Soleus (so'le-:us). Pertaining to sole (named from insertion to undersurface of heel). 113 A STUDY OF THE VOLUNTARY MUSCLES Plantaris (plan-ta'ris). Similar to above. 91. Popliteus (po-plit'e-us). Pertaining to space behind the knee. 92. Tibialis anterior. On anterior aspect of tibia. 93. Extensor digitorum longus. Long extensor of digits. 94. Peroneus longus (per-o-ne'us). Pertaining to long muscle over fibula. 95. Peroneus brevis. Short muscle on fibula. 96. Peroneus tertius (ter-she'us). Third of fibular group. 97. Flexor digitorum longus. Long flexor of digits. 98. Flexor hallicus longus (hal'ik-us). Long flexor of large toe. 99. Tibialis posterior. Posterior to tibia. Dissection and identification The dissection may well begin by a study of the calf muscles, which insert to the heel bone as the tendon of Achilles. These are the powerful extensors of the foot and make up the gastrocnemius complex. The gastrocnemius proper consists of a lateral and medial head, which meet behind in an indistinct line. These heads are more widely separated above and should be peeled apart to reveal a strong round muscle enveloped between them, the plantaris. Another muscle, the soleus, also contributes to the formation of the tendon of Achilles. The soleus arises from the lateral surface of the head of the fibula and passes back under the lower part of the lateral head of the gastrocnemius. The insertion tendons of the soleus and gastrocnemius form a sheath enclosing the cord-like tendon of the plantaris, which passes through a groove at the back of the calcaneus and becomes complicated with a small flexor of the digits. In man it inserts with the other extensors of the foot to the calcaneum. The popliteus is a triangular sheet of muscle passing from the lateral epicondyle of the humerus to the undersurface of the tibia on the medial side. Its outer surface lies next to the semitendinosus and gastrocnemius. The action appears principally to be inversion of the foot by medial rotation of the femur. Flexion of the foot is effected principally by the tibialis anterior and peroneus longus. The former occupies the lateral side of the tibia, where it overlaps the extensor digitorum longus from which it should be separated. The tibialis anterior arises from the upper lateral aspect of the tibia and inserts to the lateral aspect of the first metatarsal. Peronei muscles occupy the fibular aspect of the shank. The peroneus longus is a slender tapering muscle extending 114 108 FUNCTIONAL ANATOMY OF THE MAMMAL from the lateral aspect of the proximal head of the fibula. It inserts by a small tendon passing through a groove on the lateral aspect of the external malleolus at the ankle. The tendon then turns mediad to reach the bases of the metatarsals on their upper surfaces. Extension of the digits is produced by the extensor digitorum longus and peroneus tertius. The extensor longus arises on the lateral epicondyle of the femur and passes under the tibialis anterior to reach the ankle, where it bends through a fibrous loop of ligamentous tissue and passes over the upper surface of the foot. The tendon diverges into four parts, eventually to reach the phalangeal bones. The peroneus tertius lies directly under the peroneus longus and extends over about two-thirds the length of the fibula. It inserts into an extensor tendon of the fifth digit. The peroneus brevis may now be identified as a short muscle beneath the other peronei. Its tendon passes around the back of the external malleolus to reach a groove on its ventral aspect. It is an accessory extensor of the foot, as is the tibialis posterior. This latter is a slender muscle lying beneath the flexor longus digitorum and between it &lid the flexor longus hallicus. The tibialis posterior arises from the medial surface of the head of the fibula and adjacent aponeurotic fascia and inserts to the scaphoid and middle cuneiform tarsals. Flexion of the digits is performed by the flexor digitorum longus, which in the cat is combined with the flexor hallicus longus. The two muscles lie immediately against the ventral surface of the tibia and fibula and are partly covered by the soleus and popliteus. The heads of the two flexors are recognized as distinct parts that combine into a single insertion tendon. The common tendon diverges to the digits. The combining of these two muscles is associated with the vestigial condition of the hallux in the cat. The tibialis posterior lies along the medial border of the combined flexors. PRINCIPAL MODIFICATIONS OF MUSCLES IN MAN The increase in size of the gluteus major in man and its backward shift in position are associated with lifting the body from a sitting or squatting position and in holding the femur well extended in maintaining an efficient center of balance. Eversion and inversion of the foot in man appear to be functions originally associated with the ancestral arboreal habitat and the use of the foot in climbing. The peroneus group of muscles in man are considerably modified to aid in these functions and &lso act in supporting the arch of the foot. Similar requirements are not present in digitigrade types of feet. 115 A STUDY OF THE VOLUNTARY MUSCLES 109 Principal muscles of the. thoracic appendage which are highly modified in man are the deltoids, pectorals, and trapezius. The deltoids have shifted forward in man to pass mostly over the front of the humerus at the shoulder to act more as extensors and abductors than as adductors and rotators. The pectoralis muscles of man have become greatly reduced structurally, and the insertion is to both the proximal portion of the humerus and the coracoid process of the scapula. The higher insertion of the pectoralis group became necessary to allow greater range in abduction and extension of the humerus, which stretches these muscles. The trapezius of man, like the deltoids, converge to a smaller area of insertion and appear as slips of a rather continuous sheet of muscle. Development and innervation Muscles are strikingly adaptable and responsive to the kind and amount of work they are called upon to perform. They diminish in size (atrophy) when not used and overdevelop (hypertrophy) under conditions of heavy continuous work. The change in size of the muscle as a whole is due to decrease or increase in the size of the separate muscle fibers, not in the loss' or gain of new ones. When the innervation of a muscle is nonfunction because of mechanical injury, nervous lesions, or in infantile paralysis, the muscle rapidly atrophies and may practically disappear in the course of time. Muscles receive their innervation early embryonically. When an embryonic premuscle mass possesses a single nerve and subsequently divides into separate parts (as in the case of the deltoids innervated by the axillary), each of the divisions carries a branch of the nerve with it. This allows us to identify relationships that are not obvious. Because of this integrity of innervation, we are reasonably certain that the clavodeltoideus of the cat is closely related to the other deltoids because it is innervated by a branch of the same nerve (axillary). From its position it appears to be related to the trapezius rather than to other deltoids. Anomalous muscles and unusual slips may usually be identified as to their formation and relationships from a study of their innervation. STUDY LIST OF MUSCULAR ACTIVITIES From the study of the cat and from references on human anatomy, determine the muscles that are essentially involved in the following activities. Apply to your own body by imitating the actions. Attempt to determine the sequence of activity where more than one group is involved. 1. Abduction of the arm (raising the arm to the side-horizont~l position). 2. Horizontal circumduction of arm (carrying the arm to a forward-horizontal position from a side-horizontal position). 3. Medial and later'll rotation of the upper arm at the shoulder~oint. 4. Flexion of the elbow joint as in chinning a bar and as in lifting a weight. 5. Supination of the forearm as in tossing a horseshoe. 116 110 FUNCTIONAL ANATOMY OF THE MAMMAL 6. Adduction of the scapulae as in drawing the shoulders back. 7. Pronation of forearm as in smoothing a paper. 8. Arm movements as in serving a tennis ball. 9. Movements of arm and shoulder as in throwing a ball. 10. Movements of arm and shoulder as in rowing a boat. 11. Extension of the hip and knee joints as in rising from a chair. 12. Elevation of the mandible as in biting. 13. Depression of mandible as in opening mouth. 14. Flexion of the femur as in kicking a football. 15. Extension of the knee joint as in kicking a football. 16. Muscles used in "take off" in standing broad jump. 17. Inhalation, i.e., taking a deep breath. 18. Exhalation, i.e., expelling the air from the lungs. OTHER PROBLEMS It is suggested that a study of the brachial nerve plexus follow the muscle study. Wnen a study oi tne bracnial plexus Zor otner nerve piexi) nas been maae, ae'termine the activities that would be affected by injury or division of the different nerves, e.(j., axillary, suprascapular, radial, median. Complete division of a nerve results in complete paralysis of the muscles that the nerve supplies. Axillary paralysis refers to complete inability of deltoid action; musculocutaneous paralysis prevents flexion at the elbow joint; etc. 117 Chapter V A SURVEY OF INTERNAL ANATOMY A MID-SAGITTAL section of the head and pharyngeal region serves very well as a beginning to the study of internal anatomy. This section is most instructive in exposing the anatomical and functional relationships of the mouth, pharynx, esophagus, and larynx. These are the principal parts concerned with the control of food with respect to respiration. Other important structural features are exposed in this section, and the student should make the study mostly from the standpoint of regional anatomy. In the further survey of internal organs, attention should be directed principally to the interassociations of the systems. The dissection here should be limited to exposing the relationships of the various parts without disturbing the interrelations. This survey is preliminary to a more detailed examination of the systems and is intended to help prevent accidental destruction of important features of the anatomy when the systems are considered as separate divisions. SECTIONAL ASPECTS OF THE HEAD AND PHARYNX Mark out a line of incision in the exact mid-line of the head, and carry the line back to the first few cervical vertebrae. By means of a bone saw (a machinist's hack saw is effective), cut directly through the cranial portion of the skull to split it between the upper incisors anteriorly and in line with the spinous processes of the vertebrae. The tongue and lower jaw should be included in the section, which should be carried back to the third or fourth cervical vertebra. Spread the two sides apart, and wash thoroughly under a tap. The exact mid-sagittal section in the nasal region strikes the mes-ethmoid bone; in the brain case, the section passes through the deep depression between the cerebral hemispheres into which the tough covering membrane (dura mater) of the brain extends; in the spinal cord, the mid-point is occupied by the central canal. Orient your section with respect to these landmarks to determine how far off center the sectiun may be. 111 118 112 FUNCTIONAL ANATOMY OF THE MAMMAL The skull bones involved in the section should first be reviewed. Locate the frontal and sphenoidal sinuses, the former enclosed by the frontal bone and the latter by the presphenoid on the floor of the brain case. Observations should be made of the pituitary fossa (sella turcica) in the basisphenoid bone; the mes- and lateral ethmoids, cribriform plate, tentorium cerebelli between the cerebrum and cerebellum; and the palatine bone which forms most of the hard Frontal Pituitary 9 1and Sphe.noidal sinus Lateral ethmoid ~~~$ Mandibular. H ar d symp hysls palate Palatine tonsil FrG Sagittal section of the head of t he cat. Note particularly the rela tion of the alimentary and respiratory tracts.. palate in the roof of the mouth. Note the extension of the soft palate and its posterior curtain-like fold, or velum. Observe the difficulty involved in reaching the pituitary gland surgically through the roof of the mouth and floor of the brain case. The mouth region is divided for convenience of description into the oral cavity and the buccal cavity. The oral cavity is bounded laterally and in front by the teeth and extends back to the velum of the soft palate. The buccal cavity occupies the space between the teeth and the cheeks and lips. It is capable of considerable distension. In some rodents it serves as a pouch in which food is transported to a hiding place. These cavities are the first divisions of the digestive tube. In addition to housing the tongue and teeth, they receive the ducts from the salivary glands.

119 A SURVEY OF INTERNAL ANATOMY 113 Types and numbers of teeth are represented by formulas. In the case of most mammals, two sets appear: deciduous, or milk, teeth, and the later or permanent set. The permanent teeth of the cat are in number. The dental formula represent.s a lateral half, upper and lower, and indicates the number of incisors, canines, premolars, and molars, respectively. Incisors of the cat are poorly developed. They are best developed in the rodents. The canine, which is separated from the last incisor by a considerable gap (diastema), is a flesh-tearing tooth of considerable importance to Carnivora. The premolars and molars are grinding teeth, and their degree of development indicates their relative unimportance in the carnivores. The eminences or sharp points are sometimes referred to as the fangs. All the teeth serve in the mechanical or physical preparation of the food for efficient chemical action of the digestive juices, as well as in preparing it for swallowing (deglutition). The deciduous teeth of the kitten appear 2 or 3 weeks after birth. Permanent teeth begin to replace these at about 7 months. These really are developed very early beneath the deciduous dentition and gradually forge to the surface. Although the teeth are tjet in deep cups (alveoli) of the jaw bones, they arise similarly to the exoskeletal structures, i.e., nails or claws, and show close homology with the placoid scales of sharks. The tongue is anchored at its base to the bony hyoid apparatus previously described. The free extension of the tongue occupies the oral cavity. It is supplied with extrinsic and intrinsic musculature, which affords its movement both as a whole and in bending itself. The hyoid apparatus may be felt in your owp. body by forcefully pressing the fingers above the voice box (larynx). When swallowing movements are made, the hyoid is drawn craniad and is adapted to allow for considerable free movement to the tongue. When the tongue is protracted, the hyoid is carried forward and upward. A mucous membrane envelops the musculature of the tongue and forms a fold of attachment on its ventral surface, the frenulum. linguae. The mucous membrane continues as the soft floor of the mouth to insert at the gums. The tongue is bounded behind and above by a catilaginous flap, the epiglottis, which guards the respiratory openihg, or glottis. The opening appears as a narrow slit between elevated lips and leads into the larynx, or voice box, which continues into the trachea. The undersurface of the tongue

120 114 FUNCTIONAL ANATOMY OF THE MAMMAL is relatively smooth, but its upper surface bears numerous elevations, or papillae, which give it a rough appearance. The papillae have been described as being of four general kinds: (1) vallate, (2) fungiform, (3) conical, (4) lenticular. The flattened lenticular papillae occupy the most caudal position near the root of the tongue and are large soft projections. Anterior to these are those of the vallate type which are roughly arranged in a V -shaped pattern with the apex pointing backward. As the name indicates, each of these papilla is set in a depression. The fungiform papillae are small and numerous and occur most abundantly along the sides and near the tip of the tongue. Each papilla has a small enlargement near its tip. Conical papillae are extremely numerous. Some are rather small, but many are large, sharply pointed, and somewhat cornified or horny in texture. These latter serve as rasping structures. Most of the taste buds are located in the vallate papillae and in the fungiform type along the sides of the tongue. Submaxillary and parotid salivary glands have previously been described as to position with reference to the superficial muscles. The lower border of the parotid (which surrounds the base of the ear) is extended down to the margin of the masseter muscle on the side of the cheek. This lower extension gives rise to its duct (Stenson's), which passes forward across the masseter to the angle of the mouth. At the angle of the mouth it penetrates additional salivary tissue, the small buccal glands, and opens into the buccal cavity opposite the third premolar. The buccal glands open by numerous small ducts near the same region. The submaxillary gland (behind the angle of the jaw) overlies the sublingual salivary gland. Both are rather smooth and nodular in appearance.. The duct of the submaxillary (Wharton's duct) lies rather deep. This duct runs parallel with that of the sublingual and somewhat dorsad to the anterior facial vein. Both pass to a point somewhat below the angle of the mouth, where they penetrate to open at small papillae on either side of the frenulum linguae below the tongue. They may enter the mouth together. The rather prominent, superficial lymph nodes that lie along the anterior facial vein (usually one above and one below the vein) should not be mistaken for salivary tissue. Microscopically they resemble the salivary glands, but the histological differences are marked.. In addition to the four pairs of salivary glands now described, salivary tissue is also present just inside the cra:r.;tial portion of the zygomatic arch, between it and the eye. This fifth pair is known as the orbital, or zygomatic, gland. It is rather difficult to reach,

121 A SURVEY OF INTERNAL ANATOMY 115 and its duct opens just behind the upper molar. The salivary glands actively secrete salivr, containing the initial digestive enzyme (ptyalin) which starts the conversion of starches into simple sugars. The mucous membrane investing the palate of the cat is thrown into ridges that curve transversely across. From the soft palate extending from the sides of the palatine bone to the base of the tongue are two folds of membrane that diverge from above to reach the floor of the mouth. These folds are known as the anterior and posterior pillars of the fauces. In between these pillars on either side, the palatine tonsil is partly imbedded. The pillars form the, lateral margins of the aperture of the oral cavity into the pharynx. The pharynx The oral cavity leads directly into the oropharynx through the isthmus of the fauces. The pharyngeal extension above the palate is the nasopharynx. This converges with the passageway from the mouth (oropharynx) back to the region of the glottis and esophagus, which is described as the laryngopharynx. The paired respiratory passageways extend over the scroll-like ethmoids through the nasal region and open caudally by internal nares into a common channel, the choana. This channel is directly continuous with the nasopharynx. The Eustachian tube openings from the middle ear also open into the nasopharynx and should be observed on the dorsolateral walls. From these studies, the pharynx is seen to be a complex anatomical region with communications of varied functional connections. In all, seven communications occur: viz., the isthmus of the fauces, two internal nares, two Eustachian tube openings, the glottis, and the esophagus. In man particularly, variable amounts of tonsilar tissue occupy the pharyngeal region. A mass of such tissue is located near the Eustachian tube opening. This mass is commonly known as the adenoid tonsil. One of the functions of the tonsilar tissue is to prevent the invasion of harmful organisms by way of the pharynx. These tissues typically possess deep crypts into which bacteria may be swept, but they are frequently infected by the organisms intended for destruction. Tonsils are chiefly composed of lymphoidal tissue which gives rise to certain of the white blood cells (lymphocytes), and they also act as filtering systems for traversing lymph. From the standpoints of embryology and comparative anatomy, the pharynx passes through the most amazing changes. The numerous changes that conform with the shift from an aquatic to a terrestrial existence form a considerable part Q,f comparative anatomy. The gill region of a fish represents the primitive condition of the pharynx, and the modifications having to do with respiration, food passage, gill support (arches), and the vascular

122 118 FUNCTIONAL ANATOMY OF THE MAMMAL sion of the nervous system (see pages 184 to 1.89). Each half of the brain should be removed carefully with as much of the roots of the cranial nerves as possible. It should be hardened in 5 per cent formalin solution for later study of details. BODY CAVITIES, MEMBRANES, AND VIi:;CERAL ARRANGEMENT A general survey of the body cavities serves as a further introduction to the internal systems, and observations of structures should,.. Heart Ant.sup w.s~)"jne FIG Position of the viscera in r ~ l ation to the skeleton in the human female. Jones, courtesy o/s. H. Camp and Company.) (By Tom first be made with a minimum of dissection. Careful study should be made of the normal positions and relationships of the organs and also of their supporting membranes or mesenteries. These membranes should not be destroyed or detached until -iheir relationships have been carefully noted, and then only if their presence interferes with necessary observations.

123 A SURVEY OF INTERNAL ANATOMY 119 Dissection of body wall The peritoneal space (abdominal cavity) may have been penetrated in the muscle study or by the preparator. In any event, the upper limits of the abdominal cavity may be determined superficially at the area of the costal angle (angle of the ribs). From this region, the thoracic cavity extends to a point slightly anterior to the first rib. A line of incision may be carried from the lower abdominal region slightly to one side of the linea alba (ventral mid-line) to the costal angle. The incision is best made with scissors to prevent cutting deeper than the body wall. The wall, when opened, can be held up with the fingers while the incision is being carried along. The thorax may be opened by continuing the abdominal incision craniad. First, determine the ex&ct position of the sternum. Carry the thoracic incision forward to miss the sternum about a centimeter from the mid-line and in line with the abdominal cut. This incision will carry through the heavy musculature of the ventral thoracic wall and the costal cartilages. These are rather easily cut with heavy scissors. When the incision reaches the first rib, care must be taken to avoid damage to a large artery (subclavian) that crosses directly craniad to it. Carry the incision closely around the first sternabrae (manubrium) through the pectoralis musculature, and turn sharply to the mid-line on the ventral aspect of the neck. Expose the trachea and larynx by means of blunt dissection, separating the muscles in the ventral mid-line of the neck. Clear the fascia on either side of the trachea to expose the sheath of the carotid artery along which also passes the vagosympathetic nerve. Closely applied to the trachea and extending from the larynx are the paired lobes of the thyroid gland, each about 2 cm..long. Usually the parathyroids, which appear on the doromedial aspect of the thyroid, may be observed only partly imbedded in the thyroid tissue. Parathyroid bodies appear as small light-colored nodules. The lobes of the thyroid gland sometimes lie considerably dorsad and ~sually appear completely separate from each other. The two lob~s in man are connected across the front of the larynx by an isthmus of the thyroid tissue. The sex of the specimen should be determined before sectioning the body wall very far caudally, if this has not previously been done. In case the animal is a male, a prominent scrotal sac containing the testes may be located below the anus. The absence of a scrotum is not entirely conclusive that a specimen is a female because castrated males are rather common in laboratories.

124 120 FUNCTIONAL ANATOMY OF THE MAMMAL If the specimen possesses testes, the spermatic cords should be located. These cords extend from the testes and carry the sperm duct (ductus deferens), spermatic blood vessels, and spermatic nerve. They pass over the lower inguinal region just beneath the skin and lie rather close together at the region of the ischiopubic Su p. Vena cava Rouricle of heart R vlzntridt --,-- C\.jstic lobct--, of livu Gall bladder---- ~.,..;;;;C~ R. Kidne'1 --- Smail intestine ~-._ bladder - ; r?'o""'--"_' Urdhra -_ -_ P~ostate '1'and =,... Urinar~. j,'" S'1mph'1sis pubis" (cut) / / I / Peni.s I. CowI'er$91and Arch of oorta Lobes of r. lu"'1 Diaphroqm (cut) Inqu~nal conal.... remora I canal.---femora! artery "... " and vein ;,. Spermotic col"d.. Testis -. ~- M. Sartoris --M. Gracilis FIG pen body cavity of the cat. (By John F. Trainor.) 125 A SURVEY OF INTERNAL ANATOMY 121 symphysis. They should be freed from the skin and fascia and traced to the inguinal canal of the abdominal wall through which they pass to reach, the abdominal cavity. Carefully separate the cords and clear them of fascia to avoid cutting them accidentally in later dissection. Again locate the position of the ischiopubic symphysis, and carry an incision through the thick musculature covering it. If the symphysis is met exactly in the mid-line, it is usually not difficult to separate the union with a heavy-bladed scalpel. The union in the female is less ossified than in the male and, therefore, much easier to separate. Care should be taken to cut no deeper than through the bone. The outlets of the alimentary canal and genito-urinary systems lie close to the symphysis to pass through the internal ring of the pelvis. The original incision of the body wall may now be brought back to meet the posterior incision. Note that the abdominal wall at the posterior brim of the abdominal cavity is slightly strengthened by an extension of fascia joining the thigh. The fascia extends from the symphysis toward the forward margin of the ventral surface of the ilium. In man the thickened fascia assumes greater importance and is called the inguinal, or Poupart's, ligament. The erect posture of man causes the abdominal viscera to sag into the floor of the pelvis. The inguinal ligament aids the abdominal musculature in supporting the viscera. In inguinal hernia (rupture) a portion of the intestine enters the inguinal canal and may push into the scrotal sac. Pleura and peritoneum By slightly separating the cut edges of the thoracic wall, observe the median longitudinal partition of pleura which separates the two lung cavities from each other. This is the mediastinal pleura and consists of a double fold; the folds diverge to pass around each side of the pericardial cavity. The folds then unite again dorsally to enclose the pericardial region. The body wall can be further pulled laterad by cutting the diaphragm, which separates the thoracic organs from the abdominal viscera, Pull the side of the thoracic wall not bearing the sternum laterad, and push the viscera away to observe the inner surfaces of the ribs. Nick the ribs with a sharp scalpel in a straight line near their dorsa: curv~ture. They usually break easily when nicked, and allow the side to swing down like a door on a hinge. After a 126 122 FUNCTIONAL ANATOMY OF THE MAMMAL study of the median or mediastinal pleura, the other wall may be treated likewise. Transverse incisions through the body wall back of the diaphragm should also be made. Esophaqus ~_--i\- L pleura I cavity L~~:j:.~_..l\ 1i-Dorsal mediastinal pleura,,*- ;It-_-;"\-Viscera I pleura J!\~~~~~~f!I----t--tt- In f ven a co va ;llp~~~~--t--i1- Co rd i a c lobe riqht lun 9 ~+--H--Lo6e of L I un 9 ~~~~~~--1f---H-- Mediastina I pleu ra (over pericardium) :n.,.~.", ~H<... +-t--f+--e pi co rd i u m. ~--+ll-+o=.i''t--t---h- I n d oca rd i u m ~~4i-+sT+--t""_---h1--- Per i card i a I c a vi ty #---,/-f--pa r i e to I pie u ra '~H'----t--i+- Myocardium Ventra I mediastina I '.+----",L----:fH'---- pie u ra "--r~: --jt;l--s tern u m <---::>"'7"---- Peeto ra lis muse Ie FIG Tran sverse section through the heart region of the cat to show the distribution of serous membranes. The outer covering of the visceral elements, i.e., lungs, stomach, liver, etc., is really a reflection of the same material that forms the lining of the body wall. This serous membrane is essentially similar in structure in both thorax and abdomen, but is named to conform with its position. In the thorax it is known as pleura; in the abdome n it is known as peritoneum. Where the membrane is reflected to form the surface of the abdominal viscera, it is known as visceral peritoneum; in the thorax, the lungs are covered with visceral pleura. The walls are lined with the parietal portions of the same membrane, which also forms the dorsal mesentery supporting the alimentary 127 A SURVEY OF INTERNAL ANATOMY 123 canal. On the surface of the alimentary canal, the peritoneum forms the serosa, which is united closely to the underlying tissues. Serous fluid, secreted by these membranes, serves to prevent the visceral and parietal portions of the membrane from coming in direct contact with each other. In this way it acts as a lubric::tnt bed to prevent pleural or peritoneal adhesions and also facilitates visc~ral movements. A common irritation of the pleural membranes is known as "pleurisy." Peritonitis is an infection of the peritoneum. VISCERAL ARRANGEMENTS IJ'l" THE THORAX The right and left lungs are separated from each other by the mediastinal pleura, and each lung lies in its own pleural cavity..s.i}:;o '8 1.b8.M.JaJ"t. Jj88 wj1.bit;1.ja d!:l"8d ~ ' Df. its own, the pericardium, the diverging mediastinal pleura is applied close to the pericardial tissue over which it passes. Along this mediastinal pleura, close between the root of the lung and the heart, on either side, are the phrenic nerves passing to the diaphra~ which they innervate. The nerves follow extensions of pleura that cover the diaphragm as diaphragmatic pleura. On the right side, the nerve is closely applied to the sheath of the large inferior vena cava. In this region a peculiar condition occurs in the cat where a reflection of pleura appears to curtain off the small posteri()r, or cardiac, lobe of the right lung. This sheet of pleura is carri~d back during the formation of the inferior vena cava, which comes to lie in a dorsal position. The mediastinal pleura may now be detached from the sternum together with the pair of internal mammary arteries and the internal mammary vein which pass to the sternal surface of the body wall. Expose the heart by slitting the pericarctium. Note that the pericardium is attached only at the forward margin (base) of the heart and around its large vessels. The thymq.s gland lies in the mediastinal area or space anterior to the heart ftnd under the sternum. It consists of rather soft and scattered gla1idular tissue, but may not be evident in the older specimens. The heart and the large vessels of the heart also lie in the mediastinal SPace between the reflections of pleura forming the mediastinal portions. It is seen that the thorax really contains three potential cavities or spaces, the two pleural and the pericardia!. Fascia and fat may be cleared away for closer observation of the large vessels and nerves. Care must be taken to avoid damage to the numerous nerv'es and vessels within 1jhe thoracic area, and they should be cleared sufficiently to be easily recognized later. Much 128 124 FUNCTIONAL ANATOMY OF THE MAMMAL of this work is best done with the fingers. The thymus tissue may also be removed with the fat and fascia. The vagosympathetic trunk, at least on the left side, should be carefully followed toward the thorax and its divisions sufficiently exposed to prevent injury to them during later dissection. It is most easily located along the carotid artery in the neck region close beside the trachea. SURVEY OF STRUCTURES OF THE ABDOMEN The reflections of the peritoneum are much more complicated than those of the pleura, for the structures of the abdomen are more numerous and eccentric in position. Most conspicuous of the modified mesenteries is the large fat-laden apron that covers the abdominal viscera. This is the great omentum. The dorsal mesentery is the primary support for the viscera. The liver, the largest glandular structure of the body, and the stomach occupy the position directly beneath the diaphragm and are partly protected by the thora9ic basket. The lobes of the liver are divided into two unequal areas by a broad or falciform ligament which passes ventrally from its origin on the dorso-anterior margin of the diaphragm. It is formed by two folds of peritoneum which act in a suspensory capacity. Other attachments of the liver will be noted later. Unless the stomach is abnormally distended, it is mostly obscured by the liver where the lobes form a posterior concavity. Note carefully the attachment of the great omentum from the outer, or greater, curvature of the stomach, and find the elongate darkcolored spleen supported in the omentum. The great omentum is a double fold or sac but really consists of four surfaces of peritoneum, since a serous membrane covers each surface of the two folds. It is formed from the dorsal mesentery during the elongation and rotation of the stomach. In fact, at all points regardless of how folded the peritoneum faces a similar layer where a space intervenes. In life, the spaces and cavities created by dissection contain only serous fluid. The cavities are properly defined as the areas between visceral and parietal pleura or peritoneum. Therefore, the viscera do not actually occupy the cavities, which are merely potential spaces. In this interpretation, the cavities contain a small amount of serous fluid. Incisions through the body wall create the condition of cavities seen in dissection. The extension of omentum supporting the spleen is sometimes referred to as the gastrosplenic omentum, and it attaches to the 129 A SURVEY OF INTERNAL ANATOMY 125 spleen at its hilus, or concave margin. From the posterior concavity of the liver to the point where the stomach continues into the intestine is a third division of mesentery known as the lesser omentum. The bile duct, the hepatic artery, and the hepatic-portal vein lie between folds of the lesser omentum. The lesser omentum also connects the duodenum (first division of the intestine) and the liver, All the omenta are reflections of the original dorsal mesentery. which remains most unmodified where it supports the large intestine. The great omentum will be seen to protect and insulate the numerous folds or loops of the small intestine. Here the supporting dorsal mesentery is thrown into folds to accommodate the intestine, which is much longer than the body wall in which it is suspended. By tracing the small intestine toward the stomach, a portion of the pancreas will be found invested in the peritoneum in the concave margin of the first portion of the intestine, the duodenum. Another portion of the pancreas lies caudad to the lower border of the stomach enclosed between two layers of the great omentum. The ducts of the pancreas are imbedded in pancreatic tissue and are most easily located where it is applied to the intestine. They will be described later. The small intestine opens caudally into the large intestine at right angles to it. A blind extension of the large intestine is known as the cecum. In the cat it does not bear a vermiform appendix as in man and some other mammals. The large intestine (colon) circles from the right of the mid-line, across, and down the cavity. It is roughly divisble into ascending, transverse, and descending parts. These divisions of the colon are much more pronounced in man. Carnivores typically possess a very short large intestine, since the diet tends to be highly concentrated. The kidneys lie closely applied to the dorsal body wall and are covered over ventrally by the parietal peritoneum but are not surrounded by peritoneum as are other visceral elementso They are usually somewhat obscured by fat accumulations, particularly at their cranial margins. In the fat of this region on either side and. somewhat above and mediad to the kidneys are the adrenal glands. Each adrenal body is about the size of a grain of corn and presents a more dense, nodular appearance than the surrounding fat. Because of their position, the kidneys and adrenal glands are said to be retroperitoneal., They may be removed surgically through the dorsal body wall without entering the peritoneal space. 130 126 FUNCTIONAL ANATOMY OF THE MAMMAL The urinary bladder is a pear-shaped organ at the extreme posterior region. It is suspended from the ventral body wall from the position of the umbilicus (navel) by a broad sheet of membrane, the umbilica1ligament. The neck of the bladder is usually heavily padded by a large mass of fat on each side. Caudally, the neck of the bladder extends to a constricted tube, the urethra, which passes through the pelvis. By drawing the bladder sharply caudad, the ureters are seen to enter the bladder near its neck (see Fig. 9.1). If the specimen is a male, the spermatic cord will be seen to pass from the internal inguinal ring of the body wall to form a loop across the ureter on either side to enter the urethra at a point some distance below the neck of the bladder. Other structures of the spermatic cord continue craniad in the body cavity. If the specimen is a female, the two horns of the uterus, together with the body, form a Y-shaped structure. A horn of the uterus lies on either side of the lower part of the large intestine. The urethra lies ventral to the body of the uterus. The body of the uterus continues to the vagina. At the upper extremity of each horn, just caudad to the kidney, an ovary occurs, partly enveloped in a hood-like funnel, the ostium tuba. The oviduct, also known as the Fallopian tube, continues into the horn below. The system is supported by an ovarian ligament and a broad and round ligament of the uterus. It will be seen that in the female there is a communication from the peritoneal space to the outside by way of the ostium tubae, uterus, and vagina(see Fig. 9.2). Larger vessels of the body cavity Watch closely for nerves, and do not destroy them. Carefully remove the pericardium surrounding the heart to observe its superficial characters. Note the large communicating vessels at the base of the heart. In the cranial mediastinal area, and somewhat to the right of the mid-line, is the superior vena cava. This vessel is formed by the union of the two innominate veins. The superior vena cava may be followed to the heart which it enters at the small ear-like right auricle. The inferior vena cava comes up to the right auricle from below, where it may be traced throu'gh the right thoracic area from the position where it penetrates the diaphragm. The small right phrenic nerve to the diaphragm will be seen in close approximation with the latter vein and should be separated from it. By pulling the lungs sharply to the right and viewing the left dorsal body wall, the thoracic aorta will be observed. It should be distinguished from the esophagus, which appears as a flattened 131 A SURVEY OF INTERNAL ANATOMY 127 tube. Trace the aorta around its arch, which lies dorsad to the vena cava. If the arteries are not injected with the red injection mass, they may be distinguished from veins by their thicker walls and empty appearance. Along the aorta a small beaded-like vessel containing a clear amber fluid is usually observable, but is sometimes rather deeply imbedded. This is the thoracic lymph duct, which should be carefully traced craniad. It enters the large external jugular vein just craniad to the first rib. The aortic arch gives rise to the innominate artery, which lies in the anterior mediastinal space. Near the origin of the innominate and further down is also given off the left subclavian, which continues to the left arm. The innominate gives rise to the paired common carotids, which follow along the trachea, one on either side, and also to the right subclavian. Each subclavian artery leaves the thorax just craniad to the first rib and continues through the body wall as the axillary artery. Between the left and right auricular appendages of the heart, the right ventricle forms a tapering extension, the conus arteriosus, which is the origin of the pulmonary artery leading to the lungs. By pulling the lung somewhat away from the left auricular appendage, the short pulmonary veins are seen, but they are mostly imbedded in the lung tissue. Most of the pulmonary arteries are also similarly imbedded in the lungs. The aorta below the diaphragm is known as the abdominal aorta and lies parallel with the vena cava. At about the upper level of the kidneys, the aorta comes to lie dorsad to the inferior vena cava. Innervation of the viscera (see Figs and 10.11) A preliminary examination of the sympathetic division of the autonomic nervous system should be made in connection with the general survey of the arteries that serve as landmarks to the system. It is necessary to clear fascia from the larger vessels of the body cavity in connection with dissection of the nerves if the parts are to be spared from injury or destruction in later dissection. The sympathetic cord is easily found closely applied along the carotid. artery on either side of the trachea. Here the sympathetic cord is indistinguishably bound with the vagus nerve as the vagosympathetic trunk. Although the sympathetic system is made up of paired parts, it is not strictly symmetrical. For convenience in locating the parts to be observed in the preliminary survey, the left side may be followed. First locate the vagosympathetic nerve trunk, which 132 128 FUNCTIONAL ANATOMY OF THE MAMMAL passes close along the trachea beside the common carotid artery. The sympathetic association with the vagus really begins just posterior to the tympanic bulla; but, for the present study, begin the observations about halfway down the trachea. The left vagosympathetic should be carefully traced caudad. Just in front of the thoracic cavity a small branch passes to the left and dorsally as the sympathetic cord, while the vagus portion of the trunk proceeds directly toward the heart and lungs to which it sends branches. The vagus continues to the abdominal viscera, thus passing through the diaphragm. The sympathetic portion of the vagosympathetic trunk, with which we are now concerned, usually forms a rather inconspicuous enlargement just in front of the large left subclavian artery in front of the first rib. From this enlargement, a twig passes on either side of the large subclavian artery; these twigs unite in a more conspicuous enlargement just within the thorax between the bases of the first and second ribs. This is the inferior cervical ganglion, whereas the enlargement immediately above the subclavian is the middle cervical. Delica te branches extend from the ganglia; the larger of these branches should be traced to the heart where it forms a network, or plexus. The ganglia represent accumulations of nerve cell bodies, and the thread-like extensions from the ganglia are bundles of the long processes or axons. In the thorax, the sympathetic trunk continues caudad from the inferior cervical ganglion and lies just beneath the pleura along the aorta. In some classes, detailed dissection on the autonomic division of the nervous system may not be done. However, if time permits a thorough treatment of this important mechanism, most of the dissection should be done before other systems are studied in detail. The description for the dissection is given in the chapter on the nervous system (see pages 202 to 205). SUGGESTED PROBLEMS 1. In recording respiration and direct blood pressure with physiological apparatus, a respiratory tube (cannula) is usually inserted into the trachea and another cannula is placed in the carotid artery to connect with a mercury manometer.' Work out a method whereby the trachea might be opened (tracheotomy performed) most easily. Describe the operation in terms of anatomical position and structures involved. 2. In a study of the effect of electrical stimulation of the vagosympathetic nerve on a cat under anesthesia, work out a suitable method to follow in reaching the nerve, Which muscles would be involved in blunt dissection' in reaching the nerve, and what landmarks could be followed? 133 A SURVEY OF INTERNAL ANATOMY Suppose you wished to study the effect of tying off (ligating) the bile duct: describe how it could best be reached, and name the parts involved in the operation. 4. Describe the location of the incision necessary to reach the cecum at its closest point to the body wall. Review the character of the wall musculature at that point, and demonstrate how the wall could be penetrated without cutting transversely through muscle fibers.. 5. Since the kidneys and adrenal glands are retroperitoneal, and may be removed dorsally, work out the position of an incision whereby they might be reached to best advantage. 6. Name, in order, the epithelial tissues that would be penetrated by a bullet passing through the skin between the fifth and sixth rib and lodging in the musculature of the heart. 7. Make a semidiagrammatic drawing to show the relative positions of the structures that pass through the diaphragm. 134 Chapter VI THE ALIMENTARY SYSTEM THE alimentary canal is a highly specialized tube the lining of 'which is directly continuous with the surface of the body. Skin gradually merges with the mucous lining of the canal at the mouth and anus. When considering the elongated alimentary canal and its derivatives as enclosed within the relatively short body wall, the fundamental "tube within a tube" plan of organization is considerably obscured. This plan in a simplified form is best seen in embryonic stages. The principal function of the canal is to prepare the elements needed by the body from food materials, which progressively move along, and to allow for their selective absorption into the blood stream. Materials that have been rejected by the blood have really never entered into the body composition but have merely passed through the canal. These are eliminated as part of the feces. Digestion refers to the preparation of food so that it may be utilized by the body cells. Absorption concerns the transfer of the prepared food from the canal into the blood stream. Assimilation is the process whereby food passes from the circulation through the cell membranes and intercellular spaces into the body cells where it is to be used. Although each living cell of the body must be supplied by circulation and assimilation, digestion is the primary physiological process necessary for most food utilization. The alimentary canal is structurally adapted to effect this fundamental process by its physical make-up and by the formation of chemical agents, the digestive enzymes, which change the molecular character of the food substances. In a strict sense, food may be defined as any substance required or capable of being used by the body cells for the production of energy or for the construction or reconstruction of cells and which aids in maintaining intercellular activities. All substances that pass through the canal without being absorbed by the blood, together with excess digestive juices, are known as the wastes of digestion. Certain ones, such as cellulose, however, should not be considered strictly as wastes since they facilitate the alimentation process. Faulty elimination of the wastes of digestion, which accumulate in the large intestine, may result in the formation of toxic substances through the action of fermentative and putrefactive organisms. The entire alimentary channel acts as a linear series of communicating organs to effect proper digestion, absorption, and elimination. 130 135 THE ALIMENTARY SYSTEM 131 THE ALIMENTARY (::;ANAL. The lining of the alimentary canal is mucc>us membrane, or the mucosa. l This lining in a modified form is carried into the innermost branches of the secretory areas of the pancreas and liver, which are formed embryonically as outpushings from the primitive canal. 1'he positions of the outpocketings of the liver and pancreas are marked by' their constricted ducts, which continue to communicate with the principa} channel and empty the glandular secretions into it. Next to the lining; of the canal is a connectivetissue layer, the submucosa, which binds the muscularis (a layer of muscle) to the mucosa. Outside the muscular area is the reflected peritoneum, or serous membrane. Thus, the serosa formr the outer coat of the canal. These four layers, mucosa, submucosa, muscularis, and serosa, are typically found in the canal from the lower part of th~ esophagus to the rectum but with many variations in relative importance ana with special modificatiom of the lining. The mucosa, or inner layer I1djacent to the food material, forms various small and numerous glands that are characteristically different in the various regions of the channel. Other modifications of the lining occur which serve to increase the sur-face area for absorption or tc accommodate the changes in tension created by the food passage. ThE muscularis is of the smooth involuntary type of muscle. The salivary glands are not derived embryonically from the endoderm that forms the lining of the canal, liver, arj.d pancreas, but they are alsc glands of digestion. These glands are all of a compound character; i.e., they possess numerous branches and commtmicate with collecting tubulee to a common duct. Ducts of all digestive glands may be regarded ae tributaries of the canal proper. The more tubular structures concerned with the digestion and alimentation of food are as follows: (1) mouth (bucoal and oral cavities), pharynxl esophagus, stomach, small intestine, large intestine (colon), rectum, and anus. The mechanical preparation of food by means of the teeth and its partial liquefaction by means of saliva, of course, precedes swallowing or deglutition. The mouth region and pharynx have been sufficiently described with respect to the sagittal section of the head (see pages 111 to 115). The following description begins with the esophagus. Esophagus The esophagus extends from the pharynx to the more dilated (cardiac) end of the stomach. It is a sttaight, undifferentiated tube 1 Soon after death, the lining of the alimentary canal begins to become digested by the action of its own en~ymes. If the true character of the lining is to be observed, the canal should be promptly removed, washed out, a~cl filled with a fixative. 136 132. FUNCTIONAL ANATOMY Of THE MAMMAL lying immediately dorsad and somewha,t to the left of the trachea. In the thorax it lies in the mediastinal space (between the mediastinal pleurae). Only a short part of the esophagus extends into the abdomen, since the stomach is directly beneath and closely adjacent to the diaphragm. A loose layer of connective tissue, the tunica adventitia, unites the esophagus with the surrounding parts. At its lower end where it traverses the diaphragm, somewhat to the left of the mid-line, it is expanded slightly to meet the cranial, or cardiac, portion of the stomach. The opening of the esophagus to the stomach is at this expansion and is lcnown as the cardiac orifice. This orifice is said to be surrounded by 11 specialized arrangement of elastic connective-tissue fibers with which the muscularis here forms a cardiac valve. However, this is not all actively controlled sphincter as are other valves along the canal. Functionally, the esophagus serves to convey food rapidly to the stoipach. The four layers typical of the canal, in general, are present except for an incomplete serosa. At the upper pharyugeal end, striated voluntary muscle is present in the muscular layer which only gradually gives way to the smooth involuntary type usual to tlle canal. The muscular coats perform a series of contractions that propel the food'along. These contractions occur at regular intervals, and the phenomenon is known as peristalsis. In ruminants (cud-chewing mammals) a reverse peristalsis is normal from the first and second divisions of the stomach.(rumen and reticulum). Later the hastily swallowed food material is returned to the mouth 'where it is chewed at the animals' leisure. The food then passes to another division of the stomach and continues along the canal. Peristaltic action is typical all along the alimentary canal. The mucous layer of the esophagus in many mammals bears numerous glands, chiefly of the mucous type. However, these are not present in the cat and are also said to be absent in the horse and all rodents. In these animals, the lining of the esophagus is kept moist and lubricated by the mucus and saliva from the mouth. In maj11mals feeding on dry or coarse vegetable materials the lining of the esophagus becomes considerably hardened, or cornified. When empty, the esophagus in the neck region does not retain its cylindrical form as does the trachea but becomes dorsoventrally flattened. The lining assumes a folded appearance due to the greater bulk of the distensible submucosa. Stomach Unlike the esophagus, which is concerned with rapid transportation, the stomach is constructed as 11 storage receptacle, which permits small quantities of partly digested food to pass through at controlled intervals. The stomach receives the food at the ex- 137 THE ALIMENTARY SYSTEM 133 panded cardiac end and expels it into the intestine at the pyloric valve, a sphincter marked by a constriction between the stomach and intestine. To the left of the cardiac orifice is a prominent bulge, the fundus, which may protrude upward. The greater part of the stomach as observed in a dead animal lies somewhat to the left of the mid-line. The caudal part is tapering and folds partly back upon the wider portion. This recurving part is the pyloris. In the living body the stomach possesses considerable muscle tone, and its shape is somewhat different as determined by X ray. Its shape is also sensitive to changes-in blood flow. When the circulation stops entirely, a partial collapse of the stomach occurs to result in the curved bag-like structure with a relatively large cavity. The outer rim of the stomach is known as the greater curvature, while the lesser curvature is the concavity formed above. The pyloric region in some mammals is partly separated from the cardiac region by a deep constriction. These regions are histologically different owing to the variations in the distribution of glands. In addition to the circular and longitudinal muscle fibers common to the tract, oblique bands of muscle tissue are present in the stomach, and it is capable of a more complex peristaltic action than the other regions of the canal. These actions aid in the digestion of food by keeping it more or less agitated and mixed. 'When the stomach is empty, the lining collapses into folds, or rugae. With the aid of a hand lens the openings of the numerous gastric pits may be seen. These pits in microscopic sections appear as invaginations (inpushings) of the mucosa. The character of the glands and their distribution vary in the cardiac, fundus, and pyloric regions. Although the stomach of ruminants consists of a series of four divisions, only the last of the series, the abomasum, possesses gastric glands. The others are more esophageal in the character of their linings. Gastric juice contains hydrochloric acid and the digestive enzymes pepsin and rennin. These serve to further the process of digestion, which is finally completed in the small intestine. Pepsin and rennin are prepared commercially from the lining of animals' stomachs obtained from meat packers. Rennin is a milk coagulent; pepsin helps in protein digestion. The pyloric valve is formed by a concentration of the circular muscle fibers that abruptly thin out in the first division of the intestine. Concentration of muscularis forms a true sphincter, which in this case is reflexly affected by the acic) concentration within the stomach. Together with other factors, an increase in the acidity causes the sphincter to relax, 138 134 FUNCTIONAL ANATOMY OF THE MAMMAL which allows the passage of food into the duodenum. As the term pyloris indicates, the valve here is the gatekeeper of the stomach. Small intestine Although no marked surface differentiation occurs along the small intestine, it is described as comprising three regions: duodenum, jejunum, and ileum. It should be traced caudad from the pyloric valve. Even by means of histological sections no sharp line of demarcation is found between the divisions, which gradually merge with each other. The div;sion is based chiefly on the histologic character of the lining and the occurrence and distribution of the associated intestinal glands. The lining throughout has a velvety appearance due to the finger-like projections known as villi. These numerous projections serve to add considerable surface area to the regions where the digested food is absorbed into the capillaries, which are at most only a few cells removed from the digested food. At the bases of the villi, extended pits occur which are lined with the mucosa covering the villi. These are the intestinal glands, or crypts of LieberkUhn seen in histologic sections. Even when the intestine is distended, the pits and villi retain their form to a considerable degree. The villi are said to project and retract individually. The rate of absorption appears to be directly proportionate to the rate of movement of the villi and number of them involved at any particular time. In the duodenum, an additional type of gland occurs known as duodenal, or Brunner's, glands. Instead of resembling a simple pit, these are branched and possess numerous mucous cells. The common bile duct (ductus choledochus) and the chief duct of the pancreas pour the secretions of the liver and pancreas into the duodenum just caudad to the pyloric sphincter. This position is marked internally by a small papilla. The submucosa and mucosa are interrupted here, while in their stead is the common outlet for the two ducts at an expansion, the ampulla of Vater. The posterior limit of the duodenum is poorly defined. The term was originally used to designate the first "twelve finger widths" of the intestine in the human. The jejunum is so named because it is often found empty in a dead body. Roughly, it extends as the middle third of the intestine and together with the duodenum serves as the, chief absorptiye region for food leaving the tube to be taken into the circulation... Here the action of the additional secretions received, bile, pan-:' -. 139 THE ALIMENTARY SYSTEM 135 creatic juice, and the intestinal juices_, have completed their work so that by the time food reaches the ileum most absorption has taken place. The ileum is the continuation of the intestine which terminates at the large intestine by means of the ileocecal valve. This valve allows the wastes to pass from the small to the large intestine. Gastroepiploico-+~-H- "'. Superior mesenreric -t-"'i--+w. vein FIG Upper abdominal viscera and hepatic portal vein. The cecum is the blind pouch extending at right angles to the channel of the ileum. In most rodents a relatively large and long vermiform process is present as an extension of the cecum, and this process together with the cecum may occupy as much space as the entire small intestine. The appendix of man is a relatively small vestigial remnant M such an extension; no appendix is present in the cat. 140 136 FUNCTIONAL ANATOMY OF THE MAMMAL The numerous vessels supported by the dorsal mesentery should be noted'. It is evident that the region of the duodenum and ileum is highly vascular, i.e., contains numerous blood capillaries. All the blood draining from the area is collected into the hepatic portal vein, which carries the absorbed sugars and broken-down proteins (amino acids) to the liver. The fats have been transformed by digestion to glycerin and fatty acids, which make them soluble in water and otherwise absorbable. Ftrffy a:cic/s}<forfsi These fat products are taken into Glycenn l small lymphatic vessels, which are particularly abundant in the walls of the small intestine and which forill channels traversing the supporting mesentery. A minute central lymph vessel lies FIG Diagram of a villus to show how the absorption of foods occurs. The lymph' vessels are in solid black, blood vessels, stippled. (From Wolcott, "Animal Biology.") within each villus. Because of the milky appearance of the larger lymph channels after a heavy meal of fat, the lymphatics here become known as lacteals. The lac teals are not seen in preserved specimens. These unite to form the main portion of the left thoracic duct. A large mass of lymphatic tissue will be found in the mesentery which is known as Aselli's pancreas because of an early erroneous identification that considered it as pancreatic tissue. Another conspicuous lymph node characteristically lies near the junction of the large and small intestine. By spreading and stretching the mesentery at 'this point and holding it before a light, small oval opaque-appearing ~pots will be seen. These are end organs of sensory nerves and are known as Pacini's corpuscles. This region is evidently very sensitive since an anim),! under deep anesthesia responds reflexly to sharp pulls on the viscera here. Large intestine The cecum, mentioned in connection with the ileum, is really a part of the large intestine with its terminal portion bent rather sharply back toward the ileum. Like the cecum of man it lies on the right side in the cat rather low in the abdo)llen but solllewhat nearer to the mid-line than that of the human. 141 THE ALIMENTARY SYSTEM 137 The large intestine of the cat does not exhibit the ascending, transverse, and descending portions to a marked degree since it is relatively shorter than in man. At about half of the length of the descending colon it bears to the mid-line, a region in the human known as the sigmoid flexure. The extreme caudal straight portion, known as the rectum, opens to the outside at the anus where the anal sphincter is formed by a thickened area of the circular musculature of the canal. Except in the monotreme mammals the anus is separated from the urogenital openings by a partition, the perineum, a mammalian character. Functionally, the large intestine serves as a concentrating and storage area for the so-called "was~es" of digestion. The concentrated diet of the carnivores may be responsible for its relative shortness in these forms and for the absence of the appendix, which,,,hen functional is associated with a rather coarse diet. Little if any absorption of food takes place from the large intestine. The four typical layers are present, but there are no villi. These discontinue shortly before the ileocecal valve is reached in the small intestine. The mucosa contains the crypts of Lieberktihn and small patches of glandular tissue, Peyer's patches, which are also found in the small intestine. The entire intestine of the cat is completely invested in peritoneum which forms the serous coat. The alimentary canal of the cat is a little over 4 feet and in man approximately 20 feet long. This length provides opportunity for the complete process of digestion to occur. It also allows for the essential absorption of required materials and the temporary storage of wastes. GLANDULAR DERIVATIVES OF THE CANAL The liver Although the liver performs several diverse functions, it is moit closely associated, anatomically, with the alimentary canal. But the function of the liver in producing bile for the digestive process is of minor importance ",-hen compared with its duties in carbohydrate storage and release, in the fornation of urea, and as a regulator of protein and sugar concentration of the blood. The liver possesses certain phagocytic cells that are dest~uc' tive to harmful substances, produces heparin, an anticoagulant, and in early embryonic stages forms red blood cells. In the liver of fish, the carbohydrates are stored chiefly as fats, rather than as animal starch (glycogen). The liver makes its appearance early in the embryonic differentiation of the gut as a hepatic diverticulum. This outpushing occurs just caudad to the developing stomach and becomes complicated as a many-lobed gland. These lobes in the cat are difficult to homologize exactly with those of man. 142 138 FUNCTIONAL ANATOMY OF THE MAMMAL To the right of the broad falciform ligament, which suspends the liver from the diaphragm, lies the cystic lobe. This lobe bears the gall bladder, or storage receptable for the bile. The lobe is somewhat variable but tends to be divided where the gall bladder is applied. Dorsad to the cystic lobe and somewhat to the right are two rather distinct but also variable lobes that may appear as a" single right lateral lobe deeply divided. Its caudal lobe (Fig. 6.1) extends to the ventral margin of the right kidney. The left lateral lobe extends posteriorly to approximate the left kidney. In the cleft between these lobes lies the pyloris and the first few centimeters of the duodenum, which bends sharply back. Viewed further anteriorly, in the concavity, the lobes are separated by the portal fissure, along which pass the bile duct, the hepatic portal vein, and the hepatic artery. This is at the right limits of the lesser omentum. A deep transverse fissure crosses over here so that the neck of the gall bladder lies near the middle of the cross. Directly to the left of the falciform ligament is the left central lobe, which lies between the left lateral lobe and the ligament under the diaphragm. To the left of the portal fissure and obscured by a fold of the lesser omentum lies a small, rather sharply pointed caudate lobe, sometimes called the spigelian lobe. The apex of the latter lobe is directed somewhat to the left and dorsad to the pyloric valve. On its dorsal surface the liver is partly supported by a round ligament that continues along the portal fissure. Much of this ligament represents the remnant of the umbilical vein from the fetal stage where mother and young were connected. To expose the gall bladder and the hepatic ducts they must be carefully dissected from the liver tissue. The hepatic ducts carry bile from the various lobes of the liver to the lower constriction and extension of the gall bladder, the cystic duct. The common bile duct, which opens into the duodenum, is the continuation of the cystic duct below the entrance of the hepatic ducts. These ducts are best demonstrated on a fresh specimen, where the greenish-colored bile may be forced along the ducts by the fingers. The hepatic ducts should be cleared so that the essential connections may be made out. By a special control, bile either passes directly from the hepatic ducts and down the common bile duct or may be taken up the cystic duct to be stored in the gall bladder for later use. Bile is strongly alkalin~, saponifies fats, and serves to help neutralize the acid condition of the food just entering the daodenum from the stomach. Its pigments (colors) are mostly wastes from processes 143 THE AbIMENT ARY SYSTEM f 139 not directly concerned with bile formation. Some mammals never possess a gall bladder; it is sometimes removed surgically in man. The surface of the liver is visceral peritoneum, similar in character to the serosa of the intestine. The deeper portion is pulpy, and small areas (lobules) may be seen making a compact pattern. The liver is extremely vascular since it not only is supplied by a hepatic artery, but also possesses the rich capillary network of the hepatic portal vein. Injuries to the liver are particularly dangerous because of the difficulties in stopping hemorrhage. The pancreas Along the duodenum the pancreas appears rather thin, and in places the tissue even appears scattered. It consists of two divisions, one of which is bent back upon the other to form a V-shaped Oesophagus - cardiac porfion of sfomach---- opening of -_. commonducf pancre.af/c duel small infesfine FIG The relationship of the pancreas and its duct, and the ducts from the liver and gall bladder to the small intestine. (From RO(Jers, H ubbel, Byers, "Man and the Biolo(Jical World.") structure. The duodenal portion is closely applied to the duodenum, whereas the gastrosplenic portion lies obscured by the great omentum, a posterior fold of which encloses it. Like the liver it is a derivative of the embryonic canal. The pancreas serves two important functions. The more obvious is production of pancreatic juice, an exocrine function concerned with the digestion of all three food classes: proteins, carbohydrates, 144 140 FUNCTIONAL ANATOMY OP THE MAMMAL and fats. A more obscure function is that of an endocrine organ. Small areas, islands of Langerhans, are demonstrated histologically. The cells of these areas produce insulin, which is taken up directly by the blood capillaries passing through the pancreatic tissue. Diabetes mellitus is due to a deficiency in the endocrine function of the pancreas. The chief duct of the pancreas (Wirsung's duct), although imbedded within the pancreatic tissue, is easily demonstrated by gross dissection. It empties with the bile duct into the duodenum and may be found near the bile duct at the point where it penetrates the duodenal portion of the pancreas. By carefully picking away the substance of the pancreas around this area, the main trunk of the pancreatic duct is exposed. It receives numerous branches throughout the substance of the pancreas. The smaller duct (Santorini's duct) is difficult to locate. By injecting a color mass into Wirsu~g's duct away from the intestine, the branches of the two ducts are found to anastomose (form unions) but open independently into the duodenum. 145 Chapter VII THE RESPIRATORY SYSTEM THE respiratory system, in a broad sense, is a ventilating mechanism and is designed to provide for an efficient interchange of oxygen and carbon dioxide between the air and the vascular system. In this functional interpretation, the system consists not only of the structures acting as passageways for air, but also includes the thoracic musculature operating the ribs, the ribs acting as levers, and the lining membranes into which the lungs are reflected. This constitutes a bellows system by means of which the lungs are inflated and deflated in effecting ventilation of their deepest recesses. Thus, the respiratory system is the breathing mechanism. Respiration proper is defined as a physiological process involving an exchange of gases. The exchange of oxygen and carbon dioxide between the pulmonary circulation and respiratory air in the lungs is called external respiration. The blood gives up carbon dioxide to the air in the lungs and renews its oxygen supply. The oxygen is delivered to the tissues through the capillaries, which take up the carbon dioxide to be expelled. The interchange of gases between the tissues and the blood stream is called internal respiration. As was seen in the general survey of thoracic structures, the mediastinum effectively separates the two lungs. This arrangement permits one lung to function if the other becomes collapsed as a result of puncture of the thoracic wall. If the wall is punctured, air rushes in to increase the intrathoracic pressure to that of the atmosphere. In treating pulmonary tuberculosis, air is intentionally injected through the thoracic wall into the potential space between it and the lung, thus causing the lung to collapse. This operation is called a pneumothorax. The inactivated lung usually recovers more promptly during this rest period than it would if left in a functional state. The introduced air is slowly resorbed by the body, and the collapsed lung gradually reassumes its original character and function. During fetal life, the lungs are inactive and partly collapsed since atmospheric air cannot enter them. But after the first breath is taken, the pleura covering the lungs lies in direct contact with that forming the lining of the thoracic wall. A small amount of serous fluid intervenes between the two pleurae. Since air can enter the thorax only through the trachea, this relative position is n1aintained by the pleurae regardless of thoracic changes in respiration. The intrathoracic suction is produced by increasing the 141 146 142 FUNCTIONAL ANATOMY OF THE MAMMAL pulmonary arlery T'ilh'''.t-'r~- lefl auricle ~~:,e1":f!r"1,",4 _ pulmonary veins inferior vena cava FIG The heart and lungs from a ventral view. (Rogers, Hubbel, Byers, "Man and the Biological World." Modified from Turtox Classroom Charts, courtesy of General Biological Supply Home.) Visceral pleura Potential pleural space l-t-t---=.;..,-----l--+_ Me d i a sti n a 1 pleura Diaphrogm 't i--pericardial space Diaphragmatic pleura FIG Diagram of the lungs and pleura to show their relationships. 147 THE RESPIRATORY SYSTEM 143 size of the thorax. This can be easily demonstrated by holding the breath while performing inspiratory movements. In severe inflammation of the pleura, the serous fluid increases and may be drained out to prevent it exerting too great a pressure on the heart and lungs. Such pressure interferes with the venous return of blood and causes difficult respiration. In children the lungs are clear pink in color, but in older individuals they become dark and mottled owing to the imbedding of dust p.articles in the tissues. Adhesions of the pleura covering the lung and that lining the thorax frequently occur in man, usually near the apex. The lungs of coal miners particularly are greatly discolored and frequently are almost. black. These extreme colorations are seldom seen in animals, but in those used for food, the lungs are examined by meat inspectors to determine possible tubercular conditions. COURSE OF RESPIRATORY AIR The respiratory system proper consists only of the structures that serve as channels over which air passes. Thus, it includes the nasal passageways, pharynx, larynx, trachea, and lungs into which the trachea enters, forming a tree-like series of bronchial branches that terminate in clusters of small air sacs, the alveoli. The alveoli are designed to provide an extensive surface of moist membrane through which the exehange of' gases takes place. Water is also constantly being expelled by the lungs in the form of vapor. In man, the maximum respiratory capacity may be more than ten times the minimum requirement at rest, and more than 100 square yards of thin membrane may constitute the combined area of alveoli. The sagittal section of the head should be reviewed with special reference to the respiratory passages. Beginning with the paired nasal passageways,.the respiratory system is lined with mucous membrane, which in life is kept further moistened by water vapor. Air enters the nasopharynx by way of the paired internal nares from which it passes through the nasopharynx to reach the opening of the larynx called the glottis. The larynx is the specialized upper end of the trachea, or windpipe, and is commonly referred to as the voice box. Laryngeal structures The conspicuous feature of the larynx is the presence of specialized supporting cartilages in its walls. The most prominent of these is seen on the ventral surface, the thyroid cartilage, or Adam's apple. The circular cartilage adjacent to the first tracheal ring is known as 148 144 FUNCTIONAL ANATOMY OF THE MAMMAL the cricoid cartilage. It is thickest on its dorsal surface and, unlike the other cartilages of the larynx, forms a complete ring. The epiglottis is the cartilaginous flap of the larynx guarding the opening, or glottis. Paired cartilages, the arytenoids, form the lateral walls of the opening and protfude slightly forward. The thyroid cartilage is incomplete dorsally, and the arytenoids lying beneath it are paired with internal ligamentous attachments of which the vocal cords are most important. The larynx_articulates with the hyoid apparatus and possesses ligamentous and muscular connections with it. In the cat, between the arytenoid cartilages and the base of the epiglottis are two folds of membrane extending on either side. The thicker outer ridges are the false vocal cords~ while the inner ~ more membranous folds are the true vocal cords. These are difficult to demonstrate with the larynx split and stretched out. The folds are modified by changes in the shape of the glottis so that the edges are vibrated in varying intensity by the action of respiratory air. Articulated sounds in man are made only during expiration. Thus, the function of voice and respiration are closely allied. It is said that "purring" in the cat is produced by the streaming of air over the false vocal cords. Trachea, bronchi, bronchioles, alveoli Cartilaginous rings of the trachea are incomplete on their dorsal surface where the trachea is adjacent to the esophagus. This is apparently an accommodation to the distensible character of the esophagus in swallowing. The rings are sufficiently elastic to bring the two ends together and sufficiently rigid to hold the air tube constantly open. At the lungs the trachea bifurcates to form the primary bronchi. Each bronchus further branches into the lobes as a secondary bronchi. Gross dissection does not show further details of the tubes very clearly. However, these in turn form numerous smaller branches usually referred to as "bronchioles." At the extremities of these smaller tubes, which do not possess the cartilaginous rings carried into the bronchi, are the alveoli, which occur as clusters of small air sacs. The internal arrangement of mucous epithelium lining the respiratory passages ensures the area against desiccation, or drying out. The lining of the trachea and bronchi is further provided with cilia, or hair-like processes of protoplasm, which,drive foreign substances and accumulated mucus to the pharynx. The mucous material is carried upward by the strong and rapid upbeats of these 149 THE RESPIRATORY SYSTEM 145 abundant cilia which alternate with relatively slow and weak downbeats. General features of the lungs It has been seen that the greater part of lung substance is composed of air tubes and minute alveoli; these are held together by connective tissue. The outer covering is, of course, the reflected or visceral pleura, which closely adheres to the underlying connective Body cells G 8 Lymph spaces Right heart Left heart Pulmonary circuit 02. FIG The functional relationship between circulation and respiration-external and internal. tissue. By inserting a tube in the trachea and blowing into it, the lung may be inflated and the somewhat elastic and resilient character' of the tissues demonstrated. A cast of the tubes and sacs may be made by forcing melted paraffin down the trachea with the lungs held in water heated almost to the melting point of the wax. The surrounding tissue can then be destroyed by the use of an acid which leaves the wax as a tree-like affair with the dilated terminal ending of the twigs. The left lung of the cat possesses three deeply divided lobes, which are known as the cephalic, intermediate, and caudal, from forward back. The right lung, in addition to these three, possesses the small cardiac, or azygos, lobe which projects posteriorly into the curtain of pleura posterior and dorsal to the heart. This curtain of pleura on its dorsal surface is involved with the formation of the inferior vena cava. It is advantageous to supplement a study of embalmed material with fresh lungs, which may be secured by special request from a slaughterhouse. Those of the pig or sheep are most satisfactory and should be obt~ined with the heart and the complete trachea, including the laryngeal cartilages. The fresh material may be 150 146 FUNCTIONAL ANATOMY OF THE MAMMAL compared with conditions of the cat and with the human, as described in human anatomy texts. Usually a study of the lungs is combined with a study of the anatomy of the heart. W1th hesh matey1a\ one 1'lhou.\d l)ayt1~u.hy\:y note the ~h~;ra{)tey 01 the pleura, the mucosa lining of the trachea, and the extellt of bronchioles which are supported by cartilaginous rings. The character of the cartilage (hyaline) should also be observed by making thin sections through the rings. From the functional standpoint, the close relationship of the pulmonary arteries and veins with respect to the lung tissue should be observed in considerable detail. 151 Chapter VIII THE VASCULAR SYSTEM THE vascular system involves two distinct, but intimately related, types of systems and circulating fluids: (1) blood and (2) lymph. By gross examination, the blood circulatory system is more readily observed and understood. Structures of this system, seen in gross dissection, are the heart, arteries, and veins. Only by a microscopic examination can the essential capillary network between the arteries and veins be structurally demonstrated. The circulating fluid of this system is the blood, consisting of formed elements, the corpuscles, and the liquid plasma. Blood corpuscles normally do not leave their restricting channels. The system is therefore called a closed system. However, lymph is formed as a filtrate of plasma which passes through the capillary walls into intercellular spaces and thus makes up the immediate environment of the cells. The more obscure lymph circulation originates in the intercellular spaces and is essentially a drainage system for materials that are not absorbed back into the capillaries. Areas are drained by a convergence of these spaces into lymph channels and definite vessels. Unlike the blood system, lymph vessels possess no pumping mechanism and depend on other pressures to keep drainage active. Lymph vessels are essentially constructed as a series of closely connected valves that form a specialized tube. Lymph drains toward the large veins near the upper portion of the thorax and passes through filter beds in lymph nodes before being emptied into the veins and mixing with the blood. Only the larger lymph vessels and lymph nodes may be seen in gross dissection. Since lymph is formed by filtration of the liquid part of the blood, excess filtration due to high capillary pressure or defective capillary walls produces swollen areas (edemas) by accumulating in the intercellular spaces. When blood is withdrawn from circulation, certain elements entangle the corpuscles and form a clot which separates from a clear fluid, the serum. In normal circulation the liquid portion of the blood or plasma is similar to serum, except that the serum is deprived of essential coagulating elements that have been utilized in clot formation. Serous fluids of the body cavities and the cerebrospinal fluid resemble lymph in many respects. The circulatory sy,stem serves to maintain the balance of change in the environment of all body cells. It is the transport and distributing system absorbing essential elements as oxygen, food, hormones, and water from 147 152 148 FUNCTIONAL ANATOMY OF THE MAMMAL specialized parts of the body for distribution to all living cells. It carries away for disposal the wastes of cellular activity and acts as a distributor of heat. Reactions of blood produce protection against invading organisms, and because of its multiple duties the circulatory system profoundly affects the well-being of the organism as a whole. THE HEART It has been previously noted that the heart lies in a tough membranous sac, the pericardium, the inner surface of which is a. serous Fro. S.1.-The position of heart in the thoracic skejeton. (From Eycleschymer and Jones, "Ha,ndbook of Clinical Anatomy.") membrane that faces the outer surface, or epicardium, of the heart. The pericardia! space between these facing membranes contains a serous pericardia! fluid in life. In removing the pericardium it will be observed that it attaches only around the base.jof the heart where the large vessels emerge. The cavities of the heart are lined with 153 THE VASCULAR SYSTEM endocardium, which is the same type of tissue lining all the blood vessels as endothelium. Between the epicardium and endocardium is the bulk of heart tissue, the myocardium or heart musculature. 14!:l _lntjugul", V"m '-.om. cetot1d 3.1't An:hof aorta ;,t:.::; _.=:.....;:; perrnatic art endyein.. Com. ilia c ~--~... -.,.4-4-+~ - veinand art. ~vpoqa~tr~c" _:-:- 4_. ', ",mand el't. i FIG Heart and principal blood vessels in the human female. Thy., thyroid gland; Umb., position of ~mbilfcu:;; Ul., uterus. (By Tom Jones, courtesy of S. H. Camp and Company.) Note that the apex of the he.1rt is directed to the left and lies close to the thoracic wall but that the heart does not occupy much, if any, more space to the left side than to the right. Since all mammalian heart'; are essentially similar, a general description of one' type servef our purposes here. As previously suggested, in connection with the respiratory system, a fresh heart 154 150 FUNCTIONAL ANATOMY OF THE MAMMAL with the lungs intact is far superior to preserved material in this study. The cat heart is not only small but in prepared specimens is usually stained and distorted by the colored injection mass. The superficial characters of the heart and large vessels have been described in relation to a survey of internal anatomy (see page 123 and Figs. 5.3 and 8.3). Dissection of the heart General topography. (Heart of a pig or sheep.) The heart of the pig or sheep is approximately the size of the human heart. Proper orientation can be determined from the cat dissection. Place the heart with the ventral or sternal surface up and with the apex pointed away from you. Right and left sides of the heart can be determined in two ways: (1) the apex i entirely a part of the left ventricle, and the right and left divisions are indicated superficially by a diagonal furrow followed by coronary vessels; (2) by palpating the ventricular musculature, the left side appears firm and muscular, whereas the right ventricle feels soft and flabby. The auricles appear as ear-like projections at the base of the heart. The cavity within each auricle is more properly referred to as an atrium, or reception chamber for incoming blood. The right auricle. Make a long incision through the auricle in line with the superior vena cava. Lift the edges of the flaps and observe the wide mouths of the great veins (superior and inferior vena cava) as they enter the atrium. With scissors, carry the incision downward toward the ventricle and determine the relationships between the two cavities. Note the irregular bands of muscle lining the interior of the auricular wall, the pectinate muscles. Find the coronary sinus, which receives venous blood directly from the heart musculature and which enters the auricle as a wide cavity. Locate the thinnest portion of the interauricular septum (wall between the two auricles). This area is the fossa ovalis, an oval depression marking the position in fetal circulation at which blood was carried directly to the left heart and thus by-passed the pulmonary circuit. The coronary sinus lies just above the fossa (see Fig. 8.4). The right ventricle. Carry the incision from the auricle in a straight line through the lateral wall of the ventricle. Note the three rounded flaps of membranous tissue suspended into the ventricle and held in place by tendinous cords. These flaps are the tricuspid valve. Study in detail its position, structural character, and attachments. If necessary, wash out both cavities. Note that 155 THE VASCULAR SYSTEM 151 pointed columns of ventricular muscle (papillary muscles) are continuous with the wall of the ventricle and with the strong fibrous cords (cordae tendhteae) that extend to the edges of the cusps or segments of the valve. What function would you ascribe to these structures with reference to the valve'? Observe the heavy muscu- ~ ~~l;~lavi~r. <;~~,/:Jv Inn~ or'tl' ~ - -~-- // R~nn o r(\in u t.~_ ve:'n- - ~ < coronary a l"t '. FIG Superficial aspect of the heart and large vessels in man. N ot e particularly the coronary vessels of t he heart which supply and drain its musculature. (By Tom JO'lU)S, courtesy of S. H. Camp and Compan/l.) lar ridges within the ventricle, the columnae carneae. Find the exit of blood from the right ventricle, considering the tricuspid valve as closed between auricle and ventricle. Carry an incision upward through the wall of this exit (pulmonary artery), and note that the mouth of the artery is surrounded by three membranous pockets (the pulmf}nary semilunar valve). Determine how this structure prevents a backflow of blood into the ventricle when the ventricle relaxes. 156 152 FUNCTIONAL ANATOMY OF THE MAMMAL The left auricle. Open tills auricle in a similar manner as on the right side. Before cutting on down through the ventricle, push the finger from the auricle into the ventricle and distend the auriculoventricular opening. Determine the number of veins draining into the auricle from the lungs. These openings are the mouths of pulmonary veins. In what ways does the left auricular differ from or vena cava Wall of Corona rlf -. SInus. Tricuspid valve Wallof r. ventricle Chordae.-" ",.. tendineae F IG. S.4.-The cavities of the right auricle and ventricle of t he ox. (Drawn ~)!I John F. Trainor.) the right? Note that the partition separating the auricles is membranous rather than muscular. The left ventricle. Make an incision to expose the cavity. Study the details of the mitral, or bicuspid (two-parted), valve between tills auricle and ventricle. Explore the septum between the two ventricles as to its tillckness and kind of tissue. With your finger, find the outlet of the ventricle into the aorta. In what respect is tills outlet similar to the pulmonary artery? Open the aorta to expose its semilunar valve. Find the openings of the two coronary arteries just above the valve, i.e., within the pockets. Trace these to the walls of the heart.' Observe the.tough ligamentous connection between the pulmonary artery and aorta which usually is 157 THE VASCULAR SYSTEM 153 co~ered with 8. conspicuous pad of fat. This is the ligamenttnn arteriosus, a remnant of a vessel connecting the pulmonary artery I,.., FIG Semilunar valves and coronary artery from the aorta of the ox. (Drawn by J ohn F. Trainor.) Sup. Vena cava R.Coronary -+~~~~u~~ artery AZY.9 S vein Left subclovia n artery Pulmonary artery....,i..,..... ~... Pu 1m ona ry veins AorTa FIG Semidiagrammatic view of the mammalian heart to show course of circulation. and aorta embryonically, the ductus arteriosus. If the vessel remains persistently ~pen (patent), a mixing of oxygenated and unoxygenated bl(}od occurs. 158 154 FUNCTIONAL ANATOMY OF THE MAMMAL Observe from your dissection where the following type of heart leakage would occur: (1) auricular-ventricular, (2) semilunar, (3) interauricular, and (4) interarterial. Only the more essential features of the heart have been described here. For more detailed information, students should consult special texts on human anatomy. In studying the dissected heart, emphasis should be placed on the structural arrangement of the parts and their functional continuity. The mammalian heart is essentially a double pump equipped with specially designed valves. It serves as the propelling force for two circuits of blood that do not mix in the heart. The circuit from the heart to the lungs and back is (1) the pulmonary circuit, and the circuit from the heart to all the body tissues and back is (2) the systemic circuit. These circuits act concurrently and interdependently since no more blood can be sent through the pulmonary circuit than is delivered to it by the systemic. Left carotid artery Vaqa-sympathetic trunk L. Sympathetic trun R Middle cervical 'l0n'jlion /~Lefta~r:r~CYiOn. " ""'-.Position of 1st rib 'Inferior cervical "\. 'lon'ljion \{j~;rhorocic ~e'lmenta I Cardiac -\ qanq"o accelerator " -'S h' t '- nerves Arch of aorta ii[j:_~." ympat etlc run"" Va'lus inhib,t,on V0'lus nerye +0 abdomlnol of heart ' or9 ons FIG Parts of the autonomic division of the nervous system concerned with innervation of the heart. (Only the left nerve trunks are shown.) See also Fig. ld.ld. SYSTEMIC VEINS Because of their more ventral position, it is more convenient to describe the systemic veins before considering the arteries in much detail. However, I both types of vessels may well be exposed together, since each-'vein generally has a corresponding artery. Veins are defined as vessels that carry blood toward the heart. They, therefore, make up a drainage system and should be traced from that standpoint. In the study of the heart it should have been observed that veins possess relatively thin walls compared with the arteries. Another important feature of veins is that there are numerous 159 THE VASCULAR SYSTEM 155 valves distributed internally to prevent flow away from the heart. These act throughout the larger tubes particularly to ensure a prompt venous return of blood to the heart. Veins are typically formed from converging Ext-ern 0 I ju'lular Inf. Vena cava Adreno-Iumbar:.,,., I, I... ' lew. S.S.-Principal syst:mic veins of the cat (somewhat diagrammatic). the thoracic lymph duct. See also Fig Note position of 160 156 FUNCTIONAL ANATOMY UF THE MAMMAL TABLE OF PRINCIPAL SYSTEMIC VEINS (CAT) Name of vein Termination Principal drainage, position, and tributaries Superior vena cava... Right atrium Azygos (unpaired), ~,, " Superior vena cava Innominate cephalic) (b~chio- External jugular,,i,,... Innominate / Superior vena 'cava (op_ posite firstint.ereostl1j space) Drains head, neck, forelimbs, anterior abdominal region. Is formed by union of innominates; lies on right side of vertebral column; receives small mediastinal vein usually Seen as a large vessel on dorsal body wall to the right of the mid-line; drains the W8))S DJ cnl15i'8nd anterior abdomen by means of intercostals; drains bronchi and esophagus by vessels named from drainage Paired; eaen formed by union of subclavian and exterior jugular and passes caudad; drains head and neck by jugulars and forelimbs by the subclavians; receives vertebral and costocervical which may unite and enter as one from upper rib and cervical regions Formed by union of facial veins, transverse jugular anastomoses; crosses sternomastoid obliquely; receives cervical vessels, interior jugular, cephalic vein along front of forelimb Passes caudad at side of trachea I~ternal jup.tlar... Exterior jugular (oppc)- \ site first rib) vagus, common carotid artery, and sympathetic cord; drains brain, back of head, and dorsum of neck; frequently obscure on one or both sides in embalmed mate- \ Subclavian first rib, axillary) (distal to lrmomin.afu known as Inferior vena cava..., Right atrium rial Deeper drainage of forelimb; receives vertebral usually; axillary portion chief branches are radial, ulnar, and median from subcutaneous networks, occupying position as named Begins at junction of iliacs of hind limbs dorsad to aortic forks; spirals to right to lie ventrad to aorta; passes craniad at right of middorsal line through liver and diaphra~j drains diaphragm, 161 THE VASCULAR SYSTEM 157 TABLE OF PRINCIPAL SYSTEMIC VEINS (CAT)-(Continued) Name of vein Termination Principal drainage, position, and tributaries Common iliac (variable Inferior venl!> cava as to position of union) External iliac... Common iliac Hepatic portal...., Liver, '.. Hepatic..., Inferior vena cava liver, genital and urinary organs, parities of abdominal region. Vessel tends to be variable at kidneys; renals also variable Posterior extremity by large external iliac; smaller hypogastric branch joins medially, draining lower pelvic organs, etc. Appendage by superficial femoral and deep femoral with saphena tributaries Formed near pyloric end of stomach. by union of superior mesenteric and gastrosplenic; receives other veins named from structures drained, alimentary tract, spleen, and pancreas; reaches liver in company with common bile duct and hepatic artery through omental foramen In substance of liver anteriorly; drains liver capillaries, and being far removed from the rhythmjc propelling beat of the heart they do not exhibit a pulse. In the mammals, there is but one system of veins that does not return blood directly back to the heart, the hepatic portal system. A portal vein differs from an ordinary vein in that it is formed from a set of converging capillaries, but the main stream before entering the heart is distributed by diverging vessels through an organ. The hepatic portal vein collecting the blood from the stomach, intestine, etc., redistributes the blood through a second set of capillaries in the liver. These capillaries then reunite to form the hepatic vein, which drains into the inferior vena cava. Systemic veins are properly identified only by determining the particular areas that they drain. They should be traced from the areas from which they are seen to emerge as small tributaries and should be regarded as branches of a principal stream draining eventually into the right atrium. The principal veins are tabulated and figured as they usb.ally occur; but variations are common and rare anomalies may also be encountered. 162 158 FUNCTIONAL ANATOMY OF THE MAMMAL The hepatic portal circuit This system deserves special comment also from a functional standpoint. The hepatic portal capillaries of the intestinal region absorb the amino acids and sugars that have been digested. The concentration of these substances in the blood of the hepatic portal vein at any particular time depends upon the amount of these substances present in the intestine. Since these factors are variable, it is a function of this system to stabilize the amount of sugars and amino acids that are permitted to go into the general circulation. To effect this, the blood draining the viscera is distributed first to the liver where excesses are stored or transformed into inactive compounds until occasion demands their release and utilization. Therefore blood leaving the liver through the hepatic veins carries a rather constant percentage of sugar and amino acids which is increased or decreased as conditions in general bodily activity require. To demonstrate the presence of hepatic veins it is necessary to dissect away the substance of the liver near the diaphragm and close to the inferior vena cava, which passes through it. If the veins have been injected through a systemic branch only, no injection mass enters the hepatic portal. Capillaries of the hepatic veins block the injection mass from reaching the hepatic portal vein. Therefore, unless specially injected, the hepatic portal system contains only variable amounts of partly dried blood. SYSTEMIC ARTERIES An artery is defined as any tube that carries blood away from the heart. As previously indicated, the systemic arteries carry blood from the left ventricle to all parts of the body. They are to be.. regarded as supplying areas and should be followed and identified from that standpoint. The return is by way of the venae cavae. This makes up the systemic circuit. The pulmonary circuit begins at the right ventricle; the blood is carried to the lungs by the pulmonary artery and returned to the left auricle by pulmonary veins. Observe in this connection that the pulmonary artery carries unoxygenated blood and that the pulmonary vein carries oxygenated blood. Under usual injection methods the color mass follows the type of blood carried; i.e., the pulmonary veins are injected red and the pulmonary arteries, blue. SiI).ce the heart pumps rhythmically, the propelling force is reflected in the arteries as a pulse. Smaller arteries (arterioles) reflect the pulse in a diminished form so that when the branching of the tubes reaches its ulti- 163 THE VASCULAR SYSTEM 159 mate goal, the capillaries, a pulse may not be discernible. bed here is several hundred times wider than at the aorta. The stream L.common carotid Thyrocervica I Vertebra I 1. Brach ia I ) Intercostals Pancreaticoduodenal ~'L/"""'l---Superior mesenteric Adrenolumbar '--::-Adrenal qland Midd Ie colic. Su p. hemorrhoida I Internal iliac femoral FIG Principal systemic arteries of the cat (somewhat diagrammatic). See Figs and for course of nerves in relation to arteries. 164 160 FUNCTIONAL ANATOMY OF THE MAMMAL The area where capillaries may be seen to converge from a capillary network, rather than to further diverge, is arbitrarily taken as distinguishing arterial capillaries from venous capillaries, although the capillary bed is continuous. The smaller veins formed by converging capillaries are considered as venules in the same sense that s!llaller arteries are arterioles. Capillaries do not come to an end, but act as the connecting tubes between arteries and veins. Principal arteries are tabulated according to their usual rence. Here, again, anomalous conditions may be present. are discussed later. occur These TABLE OF SYSTEMIC ARTERIES (CAT) Name of artery Usual origin Chief distribution and position Aorta... " Left ventricle Coronary(s).... Aortic sinus (at.semilunar valve) Innominate... '.. Arch of aorta Mediastinal Innominate Common carotids (right Innominate. and left) Right subclavian Innominate Left subclavian Arch of aorta Vertebral.... Left subclavian (branches similar right and left) Internal~amm8,ry (sternail Subclavian Costocervical axis (supe- Subclavian rior intercostal) Ascending arch, descending to all parts of the body To heart walls, right and left. (The shortest circuit from the heart and back to the heart by way of the coronary sinus.) To common carotids; right subclavian To mediastinum Pass craniad on either side of the trachea to supply structures in laryngeal and head regions and brain by internal division Passes to right arm, gives rise to vertebral, internal mammary, costoccrvical, and thyroid axis before leaving thorax as axillary Passes to left arm (same as right except as to origin) Passes dorsad to vertebral part, enters vertebro-arterial canal, supplies some muscles of neck, spinal cord, brain to (circle of Willis) anastomoses Arises opposite vertebral on the sternal surface; numerous divisions to intercostals, sternum, mediastinum, pericardium, diaphragm, rectus abdominis To dorsal intercostals and cervical region (IIPd,y leave subclavian as c()stat and cervical branches) \ / 165 THE VASCULAR SYSTEM 161 TABLE OF SYSTEMIC ARTERIEiS (CAT)-(Continued) N arne of artery Usual origin Chief distribution and position Thyroid axis... Subclavian Arises just anterior and on the same side as vertebral, arches forward and upward over scapula, sends branch to thyroid gland Axillary... Continuation of the sul:>- First portion of subclavian outside clavian thoracic cavity; passes over first rib into the limb where it continues as the brachial Anterior thoracic... " Axillary Sternal portions of pectoral musculature Long thoracic Axillary Lateral portions of pectorals and Circumflex (subscapula- Axillary forks to the latissimus dorsi Numerous branches: tere~ major, ris) latissimus dorsi; deltoids and triceps; supra- and infraspinatus; subscapular; and trapezius Brachial Continuation of axillary at forks Numerous branches to arm; at elbow forms two principal branches, radial, and ulnar which follow radius and ulna, respectively, to muscles of antibrachium and hand Anterior circumflex... ' Brachial Intercostal(s)... Descending aorta Proximal end of biceps brachii Arise in paired series, to deep muscles of back, intercostals, and meninges Bronchial(s) (two)... Descending aorta (at Accompany bronchi to lungs fourth intercostll.t' space) Esophageal(s)... Lumbar (first two). Descending aorta Descending aorta Celiac axis Abdominal aorta Superior mesenteric... Abdominal aorta Inferior phrenic Celiac or adrenolumb~r Adrenolumbru Abdominal aorta Renal(s) Abdominal aorta Genital(s) Abdominal aorta Inferior mesenteric..... Abdominal aorta To esophagus (anastomose) Pass between lumbar vertebra to body wall (as intercostal) Arises just below fliaphragro, chief branches are hepatic, left gastric, and splenic Just caudad to celiac; to plj,ncreas, small intestine, ascending and transverse colon To caudal surfitee of diaphragm Passes laterad to abdominal wall To kidneys; often to adrenals In male caudad through inguinal canal; in female caudad to ovaries and uterus. May be first observed at gonad and traced back Divides into left colica to descending colon and into superior hemorrhoidal to descending colon and rectum (anastomose) 166 162 FUNCTIONAL ANATOMY OF THE MAMMAL TABLE OF SYSTEMIC ARTERIES (CAT).-(Continued) Name of artery Usual origin Chief distribution and position Iliolumbar Abdominal aorta External iliac... Abdominal aorta (forks) Internal iliac Abdominal aorta (forks) Lower dorsal abdominal muscles and sartorius muscle Passes beneath inguinal ligament to thigh; gives off profunda femora to muscle on medial side of thigh, genitalia; inferior epigastric to ventral abdominal wall; continues as the femoral To pelvic wall and viscera by following branches: (1) umbilical passing ventrad to bladder; (2) superior gluteal to gluteal muscles, rectus femoris, etc.; (3) middle hemorrhoidal which passes ventrocaudad to rectum, urethra, prostate, and penis in male; in female a branch forms uterine artery to uterus, bladder, and vagina. Continues as (4) inferior gluteal. Note the caudal artery which is a continuation of the aorta to supply thc tail ANOMALIES OF THE VASCULAR SYSTEM Variations are particularly numerous in the vascular system. Some of these are extreme in character and occur only in exceptionally rare cases. The extreme and rare variations are considered as anomalies and may \ FIG. S.lO.-An anomalous condition of origin of carotid and subclavian arteries in the cat. (Seen but once by the author in approximately 1,000 student dissections.) occur only in one case out of several thousand. Obviously, most of the anomalies of the vascular system, when found in he:1'lthy adults, cause no disturbance, and many of us possess anomalies of which we are entirely unaware., \, \ 167 THE VASCULAR SYSTEM 163 vein Transverse vessel failed to develop Retained as an anomalous.~ vein FIG Failure of an embryonic transverse vessel to develop resulted in this cat having no true superior vena cava. The innominates empty separately into the right auricle. (Soon by the author but on~e in approximately 1,000 disseotions.) Two ri'lht renal veins (one anomalous) Ri9ht geni~al (1 vein ~ Anomalous terminus of left C\e~itcd 'Jein FIG, S.12.-A fairly common anomalous condition in possessing'a "renal collar." of left genital vein over the renal vein appears less common. The loop 168 1M FUNCTIONAL ANATOMY OF THE MAMMAL Although most variations in the blood vessels of adults cause no obvious difficulty to the individual, some result in considerable disability. In a condition known as a patent ductus arteriosus, the embryonic communication between the aorta and pulmonary artery fails to close, which permits unoxygenated blood to mix with the oxygenated. Some individuals so affected have difficulty performing the slightest muscular tasks, their lips appear blue, and ordinarily they do not live beyond twenty years. A delicate operation has been performed in some instances in which the ductus is tied off (ligated), which prevents the mixing of blood and allows for the assumption of normal physical activities. A review of the structure of the thorax and the mediastinal area will indicate the precision with which the operation must be made. Many anomalies occur during embryonic development wnich critically interfere with normal activities following birth in babies, and these usually cause death within a few hours or days after birtl}.. In general, any extreme anomaly in any vital system results either in prenatal death and. abortion or in stillbirths. When we follow through the complex changes that occur in the blood system during embryonic development, it is surprising that so many individuals are so similar in the final pattern rather than that anomalies do occur. Mammals pass through an embryonic history (ontogeny) in many ways parallel to the racial history or phylogeny of the Vertebrata. Since the changes that occur in reaching the adult mammalian condition are comparatively numerous and complex, mammals possess many more variations and anomalies than are common to lower vertebrates, such as fish, amphibians, or reptiles. CIRCULATION BEFORE BIRTH \ / During embryonic and fetal life, the young of mammals secure food and oxygen and give off waste products through a highly vascular structure, the placenta. This is an extra-embryonic organ that develops on the lining of the mother's uterus and is designed to permit a large capillary area of the mother's vascular system to be in close proximity with a similar capillary bed that belongs to the fetus. Thus the fetus possesses a special circuit that passes through the placenta. Outside the body of the young the vessels of this circuit consist of a single umbilical vein and a pair of umbilical arteries, which make up the essential part of the umbilical cord. The arrangement of the capillaries within the placenta allows for exchange of dissolved substances between the blood of the mother and young, but does not permit formed bodies such as corpuscles and bacteria to pass from one circulation to the other. Each new individual not only forms its own vascular mechanism, but also develops its own blood from nutrients absorbed from the mother's blood. In this way tlle fetus is protected against infection and does not necessarily form the type of blood that the mother possesrer.. 169 THE VASCULAR SYST..I!;M 165 Respiratory and digestive functions are inactive during intra-uterine life; circulation before birth conforms to these conditions. The umbilical vein conveys relatively well-oxygenated blood to the fetus which enters the body at the abdomen (the navel represents the proximal end of the umbilical cord). The vein widens in the liver as a ductus venosus and becomes associated with the portal circulation. From the ductus the blood passes directly into the inferior vena cava but a short distance from the right auricle. Here the blood apparently mixes with the more venous blood entering the auricle from above (superior vena cava). Pulmonary LV.C. FIG Diagram of the fetal heart and large ve~sels. showing the ductus arteriosus and foramen ovalis. circulation is mostly by-passed by a short circuit through the open foramen ovale in the inter auricular wall. Therefore, the blood is directed immediately into systemic circulation. Further mixing of blood occurs through the ductus arteriosus, a fetal aortic arch that connects the left pulmonary artery with the aorta. We must assume that the oxygen requirement of the fetus is relatively low in view of the mingling of oxygenated and unoxygenated blood. However, circulation in the fetus appears to be relatively rapid; this is associated with the high rate of heart beat. Closure of the foramen ovale is effected by means of curtain-like foldh that are developed before birth, and their fusion results in the formation of the fossa ovale of the heart. The ductus arteriosus degenerates into a fibrous ligamentum arteriosus. These openings apparently are functionally closed, or nearly so, soon after birth. Respiratory activity is thought to be largely responsible for the functional opening up of the pulmonary circuit and partly responsible for the functional closure of the foramen ovale and dljctus arteriosus. Complete structural closure of the openings seems to occur relatively late and occasionally not at all, as in the anomalous cases previously discussed. 170 166 FUNCTIONAL ANATOMY OF THE MAMMAL It is of interest to observe that pulsation of the umbilical arteries normally ceases soon after the lungs are filled on the first inspiration. In domestic animals, generally, the umbilical cord is usually broken at birth by the activity of the young when thrust into its new environment. In man, the cord is tied and severed an inch or so from the body after the pulse in the cord is no longer felt. The cord and placenta are delivered as parts of the afterbirth. LYMPH VESSELS AN}) NODES The largest lymph vessel is the left thoracic duct, which empties near the juncture of the left internal and external jugular veins. A main portion of the duct may be traced as draining from the intestjnal region, but. it. is best. seen where it Jies near the aorta in the thorax. The vessel here is identified by its distinct beaded appearance. Often a small lymph vessel draining from above may be seen to enter the duct near the point where it empties into the venous system. In experimental work on lymph flow, the left thoracic duct is located by following the course of the left external jugular vem. A right thoracic duct, which drains only the right appendage and right side of the head, is present but is usually collapsed and difficult or impossible to demonstrate in the usual preserved material. Since the flow of lymph is chiefly dependent upon pressure changes, massage is frequently employed to increase the flow of lymph and waste products from the intercellular areas into the larger lymph channels. After VigorOllS and continuous exercise, massage is beneficial in aiding the elimination of fatigue products to prevent soreness and stiffness. Open a lymph vessel, and observe the character of the valves. The more prominent lymph nodes are (1) Aselli's pancreas, a large mass of lymphoidal tissue lying ill the mesentery of the small intestine; (2) armpit, or axillary, nodee;; (3) and groin, or inguinal, nodes. Scattered but rather prominent nodes are common in the neck region just below the ears, the cel"vical nodes. A remarkable histologic resemblance OCCmrs between lymph nodes and such structures as the tonsils, spleen, and thymus glands. Lymph picks up intercellular materials that are not resorbed back into the blood capillaries. Infectious bacteria are also carried in the lymphatics and in reaching lymph nodes may produce an infection in them. Swollen lymph nodes indicate an infection in areas distad to them. For exll:plple, swollen cervical lymph nodes may occur as a result of infection of the teeth. 171 THE VASCULAR SYSTEM 167 the digested fats are absorbed from the intestine into lymph channels (lacteals) that converge to form the main trunk of the thoracic duct. These may be traced by feeding an animal such as a cat with butter and a fat stain, i.e., Sudan III. The cat must first be starved for some time, and since fat is slow to be digested and absorbed, a period of 5 hours or more must elapse before the red-stained fat traverses the lymph channels. The animal is opened up at this time, and the lacteals and thoracic duct usually show up to great advantage. Injection techniques are also employed to bring out those channels more clearly. General discussion In order to understand the functional character of the circulatory system, certain physical principles governing the flow of liquids should be reviewed. In a functional analysis, all the tubular mechanisms of the system, including the heart, exist only to serve the capillary beds. The essential exchange of materials between the body cells and blood stream occurs only in the capillary areas of the system. This circumstance is strikingly demonstrated in the study of the heart. Despite the volume of blood constantly being pumped by this organ, its musculature depends entirely upon the coronary circulation for food and oxygen, and the coronary arteries are the first branches of the aorta. Occlusion, or blockage, of the coronary circulation promptly results in death, and even partial occlusion is an extremely serious condition. Coronary thrombosis and embolism are related types of occlusion that cause many deaths. Thus, the capillary areas of the circulatory system are the areas of great physiologic importance and are extremely sensitive to deficiencies. Blood must be delivered to all the capillary beds under sufficient pressum to maintain a constant supply of blood to the tissues. This pressure is also essential to their eventual drainage. Pressure and velocity of blood are greatest in the large arteries emerging from the aorta. As the stream bed widens out because of the branching of the vessels, the velocity and pres~ure diminish to their lowest points in the capillary areas. Pressure in the arteries is determined by several factors of a physical or mechanical character; i.e., the principles may be demonstrated on physical material. "The principal factors that determine the pressure in the arteries are (1) the total amount of blood in circulation, (2) the rate and amplitude of the heart beat, (3) the elastic character of the arterial wall, and (4) the resistance of the lining of the vessel to the flow. The blood is distributed to various parts of the body in varying amounts according to the special needs of the parts. For example, after a heavy meal the viscera become richly supplied by blood that has left other parts of the body where it is not especially needed for the time being. This sort of regulation is effectejl through the autonomic nervous system, principally by constricting arterioles at certain areas and dilating those in areas need- 172 168 FUNCTIONAL ANATOMY OF THE MAMMAL mg the blood. The action is known as vasoconstriction and vasodilation and is produced by smooth muscle fibers in the walls of the vessels. A general vasoconstriction causes a pronounced rise in blood pressure, whereas the opposite effect occurs in general vasodilation. In experimental animals, blood pressure is determined directly by inserting a small tube (cannula) into an artery such as the carotid. The cannula is connected to a U tube of mercury with an intervening solution of citrate between the blood and mercury column of one arm of the tube. The pressure exerted by the blood forces the mercury up into the other arm of the tube, and the difference in the levels is recorded in millimeters. In man, blood pressure is determined by indirect means and is conventionally taken at the brachial artery at the level of the heart. Circulation is cut off temporarily by inflating a rubber bag around the arm which is connected to a mercury column that indicates the pressure of the air in the bag. In releasing the air from the bag, one can hear (with a stethoscope) the blood rushing through the constricted vessel at the apex of the heart beat. By observing the height of the mercury at the precise moment the blood first breaks through its restrictions, one determines the systolic pressure. The lowest ebb of the pulse is more difficult to determine accurately. This low ebb of the beat is the diastole. The difference between systole and diastole is the pulse that is lost in the capillaries. In tracing either the comparative anatomy or the embryonic development of animal forms, we deal largely with problems of how an organism can increase in size and yet keep its living protoplasm in close contact with a suitable environment. Embryonically, the systems to be precociously formed are those which bring to all cells the essentials of their existence: nutrition, vascularity, and nervous coordination. These specializations ensure that the immediate environment of each cell is suitable to the protoplasmic needs in maintaining life. Regardless of how far the living protoplasm may be removed from the raw materials of its requirements, systems must develop to supply its immediate needs. There is no other function of a system than that of serving the vital activity of protoplasm generally. This principle is well illustrated by the vascular system. SUGGESTED PROBLEMS To test your knowledge of the vascular system as a whole, trace the course of a corpuscle from one specific organ to some other organ. What is the shortest course a corpuscle could take in leaving the left ventricle and returning to the right auricle? Why could not a drop of blood be traced in the same sense one traces the course of a corpuscle? 173 Chapter IX THE UROGENITAL SYSTEM THE. organs of repr~duction a~e unique in that their function is ~rimanly concerned with the mamtenance of the race, rather than with contributing to the essential maintenance of the individual. This means that the reproductive organs could be removed from an individual surgically without producing more than secondary modifications in its particular existence. Individuals are the conveyers of generative structures and processes that reappear in the formation of new individuals from generation to generation as a continuous cyclic phenomena. Individuallife begins with the fusion of a male and female germ cell. But the germ cells that give rise to new individuals were originally living parts of the parent's body, and thus we may trace the individual to a living preindividual existence. The germ cells are formed in the gonads (testes and ovaries). However, the primordial germ cells (those first seen there in the development of the gonad) appear to arise elsewhere and secondarily migrate to the early gonad. The chromosomal character of the early germ cells determines whether the new individual is male or female. It appears to be entirely a matter of chance as to which sex the individual will be. In the same way, chance and probability determine the particular hereditary characters that will be exhibited, and each new individual is a unique being. Sexual homologues between the male and female external genitalia have been discussed in the first chapter. Many internal parts are also regarded as homologous. Thus, the testis of the male is represented by the ovary (in part). These are the primary sex organs and are responsible for secondary and accessory sex differentiation. Secondary sex characters such as distribution of the hair, muscular and skeletal conformation, and the differences in the development of the larynx in the two sexes are referable to the endocrine function of gonads and the difference in the hormones produced by each type. Thus, castration (removing the testes) of the male before puberty prevents the expression of maleness in both structural and physiopsychic ways. Castration is a common practice on domestic livestock not kept for breeding purposes (cattle, sheep, hogs, horses). The operation on animals raised for slaughter is>usually done while 'the individual is relatively young so they will fatten more readily and produce finer quality meat. Castra- 169 174 170 FUNCTIONAL ANATOMY \)F THE MAMMAL tion is usually delayed in horses until the stronger shoulder and muscular development of the stallion has begun to take place. Removal of the ovaries (oophorectomy) is performed most frequently on house pets, dogs and cats, and is commonly known as "spaying." This not only eliminates the possibility of the Itnimal having young, but terminates the occurrence of "heat periods" which are induced by ovarian activity. In approximately 600 female cats obtained from an animal refuge (in Philadelphia) only 3 had been Spayed, while in about 400 males, at least 10 had been castrated. This does not give a true picture of actual conditions, however, since most pet animltls never reach humane societies as do the unwanted "strays." Male organs REPJWJ)IJCTIVE SYSTEM This system has been partly descl'ibed in the introduction to internal anatomy (page 111) and SUIlerficial dissection (page 59). The scrotal sac should be opened by a careful incision over each testis, and the incision should be det~p enough to cut through a tough membranous sheath beneath tlle skin, the tunica vaginalis. The testis can now be delivered through the incision. Observe that the tunica vaginalis ehcloses the testis and is continuous with the spermatic cord, which passes craniad to the inguinal region. The spermatic cord t:jonsists of the membranous sheath enclosing the ductus deferell.s (sperm duct), spermatic artery, vein, and nerve. The latter tw() parts are difficult to demonstrate in a preserved specimen. The ductus deferens is readily iderltified by following the spermatic cord through the body wall whe~re the ductus is seen to loop over the ureters (from the kidneys) and pass dorsad of the urethra, which drains the bladder. In followirlg the ductus deferens t'o the testis, it is seen to emerge from an etongated mass of convoluted tube, the epididymus, lying on the sluface of the testis and connected to it. The sperm are formed in the microscopically small seminiferous tubules of the testes and pass through collecting vasa efferentia to reach the epididymis bef(\re entering the vas deferens. The character of the tunica vagina1ts and spermatic cord is best understood in following the migration of the testis from the abdominal cavity into the scrotal sac. Testes arise, embryonically, mediad to the kidneys, and a little below this r~gion they receive their blood supply and drainage (review genital arteries and veins). They then descend, carrying with them the ductus deferens. Because of their 175 THE UROGENITAL SYSTEM 171 early position in relation to the ureters, the ductus deferens crosses them in reaching the lower pelvic region. Further descent of the testes pushes them into the peritoneal lining of the abdominal cavity which envelops them as' an invagi- "..::;.~'*-Medull('J ~~':";":"';'.:L...Pelvis Epididymis Ductus deferens ~A''.JF+- r. fferen t ductules Sem'miferous tubules Section of Testis (semi dio9rammatic) Spermatic vessels Glans penis Spermatic cord :E~ididymis +-\',Hi!--Testi s Tunica va9inalis "'<lll~~ Skin of scrotum FIG Urogenital system of the male cat. nating tunic. But the musculature of the wall is not carried along; it separates to form the inguinal canal, which extends from the internal inguinal nag (seen on the inside) and the external inguinal ring on the outer surface of the body wall. By splitting the inguinal 176 172 FUNCTIONAL ANATOMY 'OF THE MAMMAL canal and drawing the testes up to their developmental position mediad to the kidney, these relationships will be better understood. In case the testes fail to pass through the inguinal canal, the condition is known as cryptorchidism and results in sterility in man and other mammals in which the testes normally leave the body cavity. If the condition is corrected surgically, fertile sperm may be produced. In the scrotal sac, the two testes are separated by a partition, the mediastinum testes. Observe that the spermatic cords are superficial and may be reached surgically by a simple skin incision. Sterilization of the male may be accomplished by a simple operation known as vasectomy. This consists of splitting the sheath of each spermatic cord, removing a section of the ductus deferens between two ligatures without disturbing the vascular and nervous connections to the testis. The operation does not interfere with hormone activity. The ductus deferens should now be followed to the urethra which it enters at a glandular enlargement, the prostate gland. The prostate nearly encircles the urethra and discharges prostatic fluid into it through a duct common with the ductus defere'ns which conveys the sperm. The cat does not possess a seminal vesicle as is present in man. In following the urethra (and course of sperm) further cauctad, a pair of rounded Cowper's (bulbo-urethral) glands are found rather deep and near the ischiopubic symphysis to which the penis is attached. These also open into the urethra by means of ducts. The penis is retracted into a fold of skin between the testes on the wall of the abdomen. The distal end bears an enlarged cone-shaped glans around the base of which the skin is attached as a prepuce, or foreskin. In the cat, the glans penis bears numerous horny spines on its surface which may be observed easily with a hand lens. A transverse section of the penis shows it to consist largely of three distinct columns bound together with dense connective tissue. Ventrally, a single column encloses the urethra as the corpus cavernosa urethra, while above are a pair of corpora cavernosa penis. These possess blood cavities (caverns), and erection is due to the blood becoming trapped in these vascular areas. The character of the attachment of the penis to the symphysis and abdominal wall causes it to become directed craniad during erection. Obviously, the penis is primarily an organ of reproduction rather than a urinary structure. The function of urination (micturition) could occur effectively with the urethra opening in some other manner. Thus, the 177 THE UROGENITAL SYSTEM 173 penis is primarily designed to convey sperm to the vagina of the female, where they may proceed directly to effect fertilization. The urethra serves both genital and urinary functions only from the point at which the ductus deferens enter. The female system The genital system of the female does not become so highly specialized as the male. The gonads (ovaries ~ remain rather close Oviduct (uterine tube). Ovary Horn of uterus Broad I i90 ment Cervix of Uterus FIG Urogenital system of the female cat. to their position of origin and lie somewhat below and mediad to the kidneys on the dorsal body wall. Ettch ovary is partly invested by peritoneum and partly hidden by a fringed funnel-like expansion of the uterine tube,~the ostium tuba. The ovaries are elongate ovoid bodies about 1 cm. long with most of their surface exposed to the 178 174 FUNCTIONAL ANATOMY OF THE MAMMAL body cavity. The ostium tuba is the part of the oviduct that receives the mature ovum that is cast from the surface of the ovary at ovulation. The oviducts (Fallopian tubes or uterine tubes) pass somewhat craniad in a convoluted manner and then descend to become continuous with the larger comuae (horns) of the uterus, which join below into a single corpus (body). This type of uterus is known as bipartite. The body of the uterus is continuous with a thinner walled vagina which terminates at vaginal vestibule. The vestibule receives the urethra from the. bladder on its ventral aspect. The ovaries are attached to the dorsal body wall by a.specialized mesentery, the ovarian ligaments. These continue craniad and caudad as broad uterine ligaments supporting the horns of the uterus. An extension of each broad ligament extends laterocaudad as the round ligament, which attaches in a position comparable with the ir~.ternal inguinal ring of the male. FIG Section of ovary of the cat. 1 free and 1', attached border; 2, connective tissue 5, early germ cells: 6, 7, 8, and 9, developing follicles. An ovum is seen in 8 and 9; 10, corpus luteum. (From Zoethout, "Text-book 0/ PhysioloOY," C. V. Mosby Company.) The horns of the nonpregnant cat are very slender and in pregnancy become surprisingly distended. The number of young in a pregnant uterus can be readily ascertained by the series of enlargements along the horns. Careful inspection of the ovaries of a pregnant cat ' shows them to possess conspicuous elevated bumps that are located at the sites of the ovulations preceding the pregnancy. These bump-like areas are corpora lutea of pregnancy and persist in an endocrine function to maintain the pregnancy. If they are destroyed early in the pregnancy, the young are aborted. Apparently, these conditions hold for mammals generally. A corpus luteum of ovulation is formed for each egg shed by the ovary, but these do not persist if no pregnancy ensues. In young females the 179 THE UROGENITAL SYSTEM 175 ovary appears smooth on its surface, but in older individuals the ovary shows scars of previous ovulations (corpora albicantia) at the positions where the eggs were. shed through rupture at the surface. FIG Pregnant uterus of cat (A) and membranes of fetal kitten (B). "General Zoology.") (From Storer, The uterus is highly vascular. When a fertilized egg is implanted, its lining (endometrium)' contributes' to the formation of a placenta through 'which the young obtains nourishment from the maternal capillaries. No direct circulation between the mother and young occurs. The capillaries of the placenta of the embryo come in close proximity to maternal capillaries, and exchange of materials takes place between them. In the human and in other mammals, an ovum may become fertilized before entering the Tube Ovary Round ligament Fundus Ovary U terine tube Ovarian artery Vagina U retel cavity Uterine Uterine artery FIG Uterus and as,;'ociated organs in the human. (From Pitzman, "Fundamentals of Human Ar>atomy," C. V. Mosby Company.) 180 176 FUNCTIONAL ANATOMY OF THE MAMMAL oviduct and implant itself outside the reproductive tract, along mesenteries or intestine. These abdominal, or extra-uterine, pregnancies ordinarily do not advance far since the blood supply is inadequate to maintain the development of the embryo in the position in which implantation has occurred. Intra-uterine life As is commonly known, the period of intra-uterine development varies greatly among the mammals. In some species, a peculiar delay in the implantation of the fertilized egg occurs; in others a different sort of delayed development is found, A table of gestation periods for some representative mammals is given below. " Ammal Gestation period Usual number of young Opossum,,,,,, days Rat days Rabbit days Dog days Cat days Pig... " 4 months Sheep..., months Monkey (Macacus rhesus)... \) months Man...,, months Cattle.,., months Horse, months Elephant.,,...,.,,...,.. " 20 months 7 to 12 6 to 7 4 to 6 5 to 7 4 to 7 6 to NEPHRIC SYSTEM The kidney of the mammal tends to be a compact bean-shaped organ. However, in some forms (as in tb.e bear and in cattle) the kidney exhibits external lobation and elongation which resemble the more primitive condition. The ureters connect with the kidney at its hilus near the connections of the renal artery and vein. Ureters carry urine to the urinary bladder, which is drained through the urethra to the outside. As has been observed in the study of the genital system, the urine at some point along the tract follows an outlet that also serves the reproductive system. In the female the common outlet is the vestibule of the vagina, but in the male the common outlet extends from the position ;of entrance of the ductus deferens and its associated parts at this point. The urethra 181 THE UROGENITAL SYSTEM 177, of the male is, therefore, more specialized and extensive than in the female. Kidneys are formed on the dorsal body wall. of the developing young and do not push ventrad sufficiently to become enveloped by the peritoneum. The position in the body is said to be retroperitoneal, since they may be removed surgically without entering the peritoneal cavity. The operation is a nephrectomy, so called from the term "nephric system" commonly used to designate urinary parts of the urogenital tract. A fibrous sheath encloses the kidneys which makes rather weak attachments to the body wall and peritoneum. A kidney may become dislodged from these attachments to produce a condition known as a "floating kidney." Considerable variation occurs in the size of kidneys in specimens of similar size. The right kidney usually lies somewhat craniad to the left, and both are usually somewhat hidden by fat deposits in a capsular mass. renal vejn-/-- main col/eding duels in.!::_.. pelvis of kidney,-,' FIG A longitudinal section through the kidney of man. (Rogers. Hubbel. Byers "Man and the Biological World." Redrawn/rom Maximow. "Textbook 0/ Histology. ") Internal structure of the kidney The functional unit of the kidney cannot be demonstrated without using the microscope on special preparations. In a longitudinal section, which splits the kidney into symmetrical halves, certain 182 178 FUNCTIONAL ANATOMY OF THE MAMMAL internal features may be observed by gross inspection. A superficial cortical area is distinguished from a more central medullary " area. The cortical portion has a somewhat stippled appearance, whereas the medulla is characteristically made up of renal pyramids, which in the cat appear to have fused into a single pyramid. In man, the pyramids taper from a broad base at the cortex to rounded apices, or papillae. The apices of the pyramids project into separate channels, or calyces, which c,onverge into a common cavity, the pelvis of the kidney. The renal pelvis is continuous with the opening of the ureter. loop offht> uriniferous fu/ju/e FIG, 9.7.-Diagrammatic figure of a renal corpuscle and uriniferous tubule. (Rogers, Hubbel, Byers, "111 an and the Biological World." R edrawn fro m Amberson and Smith, "Outline of Physiology.") The cortex is reddish brown and contains numerous renal corpuscles (approximately a million in man). A renal corpuscle consists of a tuft of capillaries, a glomerulus, projected into an enclosing renal capsule (Bowman's capsule) which continues as a renal tubule. These parts make up the functional unit, or nephron, of the kidney. Urine is formed as a filtrate of the blood through the capsule, but its purely physic ~l character is modified by activity of the cells of the tubule in connection with the blood stream. Renal tubules form convolu.tions in the cortical area and eventually open into larger collecting tubules and excretory tubules that converge to the ) pelvis and produce the striated and radiating appearance of the medullary area. 183 THE UROGENITAL SYSTEM 179 I Course of urine and structure of channels. The urine from the pelvis of the kidney follows a channel lined with mucous membrane. The ureters possess an outer fibrous coat and middle layer of smooth muscle. The bladder has a serous layer on the outside, layers of smooth muscle, and a submucosa of connective tissue joining the mucous lining. At the neck of the bladder, the circular muscular layers form a sphincter to control micturition (emptying the bladder). From the bladder the muscular coat continues into the. urethra as its outer covering (except for a fascia-like sheath), and a thin layer of spongy connective tissue lies between the muscularis and mucous lining. The female urethra is relatively short and undifferentiated. In the male the urethra from the sphincter of the bladder to the prostate gland is designated as the cystic urethra; from the prostate gland to Cowper's gland, as the prostatic urethra; and the portion enclosed in the penis, as the urethra penis. 184 Chapter X THE NERVOUS SYSTEM THE nervous mechanism is both structurally and functionally complex. It ramifies to all parts of the body to serve as the dominating and coordinating system of the organism as a whole. For convenience of study, the system is considered as being divided into three parts: (1) central, (2) peripheral, and (3) autonomic. However, these divisions are closely interdependent, and they should never be regarded as separate units of the system as a whole. Nerve tissue is 'described as the master tissue of the body, but it too is dependent for its existence upon the other tissues that it dominates. Central division The central nervous division consists of the brain and spinal cord. This part of the system is protected by the skull and vertebral column and is supplied with a special set of protective membranes, the meninges (cranial and spinal). Further protection to the central nerve tissue is afforded by a water bed of cerebrospinal fluid surrounding the brain and cord. These carefully protected central parts communicate with the environment by means of nerve fibers of the brain and spinal cord. The body is acquainted with outside conditions especially through the sense organs: olfactory, optic, and auditory, Other sensory end organs and nerves not only connect the central nervous system with external environmental conditions, but also carry impulses from internal parts so that adjustments through outgoing impulses can be made for conditions generally. Centers of the central division act in reception, transmission, initiation, or termination of impulses. Peripheral division This division consists of the cranial and spinal nerves and sensory epithelium of the organs of special sense. Sensory elements make up the receptor part of the peripheral division. Motor impulses leaving the central division pass through the effector fibers of the peripheral division to muscles and glands. The voluntary muscles are innervated by peripheral motor fibers that pass directly to them, but involuntary muscular tissue ~cardiac and smooth) and the various glands possess a double motor innervation and receive their impulses through an autonomic mechanism. 180 185 THE NERVOUS SYSTEM 181 Telencepha Ion (olfactory bu I bs cerebra I hem ispheres) Latera I ventricles (l st and 2nd) Aqueduct of Monro Diencephalon (thalamus etc.) Mesencepha I on corpora q_uadriqemina etc. Metencepho Ion (cerebellum and pons) M yelencepho I on (medu 110) Myelen (cord) FIG. lo.l.-general plan of mammalian brain. The stippled central area represents the cavities (ventricles) of the brain; heavily drawn inside lines show the linear series of division; parts in broken lines are covered dorsally by the superficial portions shown by the outside \i,,~. 1 \.\'> XII c!'3.""a\ mwve \)o~ition. \~ul>e!ncia\ connection) in relation to divisions or hrain. Spinal nerve Ventra \ bra n ch Se9mentol9an'11ion Sympathetic trunl<~!>l--",", FIG Cross-sectional plan of the nervous system. The structural connections of central, peripheral, and autonomic divisions shown ~emidjagrammatically. 186 182 FUNCTIONAL ANATOMY OF THE MAMMAL Autonomic division The autonomics include special nerve fibers and tracts of the cranial and sacral nerves (peripheral division) that reach the involuntary organs directly from the central nervous system as parasympathetics and, through another special arrangement of nervous tissue, as sympathetics. Impulses from the sympathetics may originate in the central division but pass through special centers outside the central division, the sympathetic ganglia, before reaching the parts to be affected. Thus, the involuntary organs possess two distinct sets of nerve fibers, one from either cranial or sacral parasympathetics, and one from the postganglionic sympathetic fibers. Control of the involuntary actions by the autonomics involves a constant shift of balance between two antagonistic forces; where one set of fibers act as an inhibitor of an action, the other accelerates; if one acts to constrict vessels, the other dilates them. Autonomic fibers are essentially motor or effector in character to control the secretion of glands and the activity of cardiac and smooth muscle. Endocrine organs (ductless glands) share with the nervous system the function of governing and controlling the involuntary activities of the body. Thus, we recognize chemical regulation by hormones secreted by the ductless glands and nervous regulation that is essentially dependent upon impulses coming from the central nervous system. Hormones reach all the tissues of the body by way of the blood stream, and nerves likewise ramify to all other tissues. Thus all parts of the body are under both chemical and nervous control. Investigations have shown that hormonelike substances may be formed directly from some of the nervous tissues. Therefore, the actual physiologic character of the control of the two systems may be much closer than is commonly thought. In general, however, a reaction to a nervous stimulus is extremely prompt and transitory, whereas the hormones are slower in action and more persistent in their regulatory effects. The neuron A neuron is the structural unit of the nervous system. I t is a highly specialized cell consisting of a rather conspicuous cell body from which protoplasmic processes are extended. In man, some of these processes may be more than 3 feet long; e.g., cell bodies located in the spinal cord bear processes reaching the tips of the toes. Cell bodies are located either within the central nervous system, or in compact associations outside the brain and cord, the ganglia. Bundles of elongate processes make up the nerves as such and, when associated in tracts, also appear as the white matter of the brain and cord. The gray matter is largely made up of cell bodies that are located peripherally in the brain and centrally in the cord. A process of a cell body that carries the impulse away from the cell body is known as its axon. Other processes conducting impulses to a cell body are called dendrites. Impulses pass from one neuron to another byapprox- 187 THE NERVOUS SYSTEM 183, imating, or synaptic, junctions of the processes and follow a law of forward progression. Three general types of neurons are generally described: (1) receptors, (2) effectors, and (3) connectors, or associative neurons. The receptors are also known as sensory or afferent cell types since the impulse originates outside the central division of the nervous system and is conducted to it. Effectors are also called motor, or efferent. In the latter, the impulse '.;:)IJ>mHW pr'oce,$\$ - '... ~ _. _ Li S. flavuffi - - I'"-Si1_~'_ Int",r_spinal lig ~---I Spin,,) cord PMterior long_lig_ -- --:-- FIG. 1O.3.-Detail of spinal nerve in man. Upper figure, transverse section of dorsal thoracic wall; lower figure, sagittal section in same region. (Drawn by Tom Jones, courtesy S. H. Camp and Company.) leaves the central nervous system or sympathetic ganglia and is conducted by an axon to the parts to be effected. Associative neurons are located in the brain and cord and make connections with the afferent and efferent types. The segmental character of the spinal cord and the arrangement of nerves make it possible for impulses to enter the central division and be transferred at any level, depending upon the circumstances. In the brain,..

188 184 FUNCTIONAL ANATOMY OF THE MAMMAL the serial levels are not so clear cut, and many complex centers are involved which may more strongly modify an impulse. Here an original impulse may be intensified, inhibited, delayed, or tenninated. The central system is essentially a complex of nerve tracts and centers that influences, and is "Fronta I lobe Lon']ifudinal fissure of cerebrum empora I lobe R. hemis~here of cerebellu m A l-:xn Source of Cranial nerves o If a dory tract Mammillary body. Crura cerebri-~'-4!i,""" Pons Trapezium Pituita rj Glan B Pyramidal tract FIG. lo.4.-dorsal (A) and ventral (E) aspects of the <Jat's brain. (Modified from lyiivart.) influencoo by, all the conditions of the body through its ample connections with peripheral and sympathetic parts. General features of the brain and cranial nerves The brain and cord arise tog~ther from a longitudinal thickening of ectoderm along the middorsal axis of developing embryo. This thickened

189 THE NERVOUS SYSTEM. 185 ar~a soon becomes deeply grooved, and finally a complete cylinder is formed which becomes pinched off from the overlying skin as the neural tube. Through different~ation and growth the neural tube forms the spinal cord and brain. The brain of the mammal, particularly in the primates, becomes complex because of extreme differences in the development of the fundamental parts. Because of this differentiation of parts and attendant flexures to make for compactness, the original plan or linear arrangement of the divisions is greatly obscured. For clearer understanding of the plan of the mammalian brain, the student should first study or review the brain of a more primitive form such as the shark, where differentiation of parts is not so extreme. The spinal cord is never greatly modified throughout the vertebrates generally, not only with respect to its structure, but also in connection with the arrangement of the spinal nerves. Pdrieta.1 lobe FIG. lo.5.-lateral view of the human brain. (From Francis, "Fundamentals of Anatomy," C. V. Mosby Company.) Early in development, the brain differentiates into three thickened vesicles. The three primary vesicles from posterior to anterior are known, respectively, as the prosencephalon, mesencephalon, and rhombencephalon. The brain from its early inception to the adult condition is referred to as the encephalon. The prosencephalon (forebrain) divides into two regions, the telencephalon and the diencephalon. The mesencephalon (midbrain) does not further divide, but the rhombencephalon (hindbrain) differentiates into the metencephalon and myelencephalon. These differentiations, therefore, result in the formation of a longitudinal series <?f five divisions that grow and develop at very unequal rates in the mammal to obscure the primitive linear arrangement. In the shark all these fundamental divisions may be seen superficially on the dorsal aspect, since the parts are more nearly of equal size and none is completely covered as the result of flexure or e.ixtreme specialization. The telencephalon forms the cerebral hemispheres, the olfactory tracts, and lobes; the diencephalon forms complex transfer paths between the

190 186 FUNCTIONAL ANATOMY OF THE MAMMAL cerebral cortex and posterior divisions, the thalami, the optic nerves, retitla, and chiasma, the infundibulum of the pituitary gland and the pineal body; the mesencephalon gives rise to the corpora quadrigemini, which are homologous with corpora bigemini or optic lobes of the lower vertebrates. In the mammal, the midbrain appears wedged between the cerebellum and cerebrum, although it is actually adjacent to the thalamus of the diencephalon. The metencephalon includes the cerebellum (little brain) and the pons, a transverse thickening on the ventral aspect. The myelencephalon becomes the medulla oblongata, which is directly continuous with the spinal cord. If this fundamental plan is well understood, few difficulties are encountered in a further study of details. Twelve pairs of cranial nerves are present in the mammal. These have been referred to briefly in connection with t he foramina of the cranium. The first has its sup~rficial origin (point of contact) with the telencephalon Decusso.tion Of corticospinal trocts (pyro.mids) FIG. lo.b.-ventral view of the brain stem of man to show attachments of cranial nerves. (From Francis, "Fundamentals of Anatomy, C. V. Mosby Company") as an anterior extension. The second originates from the diencephalon, the third and fourth are from the mesencephalon, and all the rest are from the medulla.. The original cavities of the early vesicles differentiate into four ventricles. The first two are the lateral ventricles of the cerebral hemispheres which communicate with each other centrally. From t he central com-

191 THE NERVOUS SYSTEM 187 m~mication extends the foramen of Monro to connect the lateral ventricles with the third ventricle, which occupies the diencephalon. The third ventricle narrows posteriorly to form a channel, the iter (aqueduct cerebri), which broadens in the medulla as the fourth ventricle. This is covered only by memhranous tissue and appears as a deep groove in the medulla when the membrane is removed. Tufts of capillaries extend into the fourth ventricle as a choroid plexus. A similar condition occurs in the roof of the third ventricle, b\lt here the corpus callosum between the cerebral hemispheres covers the true membranous roof of the diencephalon and its choroid plexus. Cerebrospinal fluid occupies the ventricles of the brain, the central canal of the cord, and the area between the meninges and neural parts. The choroid plexi are considered as serving the cerebrospinal fluid in maintaining its volume and proper constituents. THE BRAIN OF THE CAT Removal of the brain intact requires considerable time and patience, particularly if any attempt is made to spare the roots of the cranial nerve sufficiently well for their proper identifications. If the brain is to be removed intact, a circular drill-like saw (trephine) is useful in entering the cranial cavity: If the directions were followed in the survey of internal anatomy (page 111), the brain may be removed as separate halves from a sectioned head. Care sh;uld be taken to sever the roots of the cranial nerves while the brain is being gently lifted away. As much of the nerve roots should be kept with the brain as possible. The two sections may be placed together with only the pituitary and pineal bodies materially damaged if the section has followed the mid-line. Dorsal surface. Note the prominent cerebral hemispheres that make up the bulk of the brain. The paired anterior extensions are the olfactory lobes. By separating the hemispheres, the position of the corpus callosum will be seen as the thickened white band connecting the hemispheres. The roof (pallium) of the cerebrum consists of a thick layer of cells that form,the cerebral cortex. The cortex is marked superficially by fissure's (sulci) which separate convolutions (gyri). More complete fissures tend to divide each hemisphere into more or less distinct lobes. These are named with respect to the positions occupied in the cranium, i.e., (1) frontal, (2) parietal, (3) temporal, and (4) occipital. The last three lobes are rather poorly outlined in the cat. The development of gyri and sulci indicate adv41ncement since, in general, their occurrence and emphasis coincide with advanced mental powers. The obvious

192 188 FUNCTIONAL ANATOMY OF THE MAMMAL explanation of this condition is that the area of cerebral cortex"is ~ncreased by the corrugations. The cerebellum is deeply folded, which also increases the area of gray matter. It is made up of a median lobe, the vermes, and a pair of lateral lobes. By gently separating the cerebrum and cerebellum, the corpora quadrigemina are exposed. These are seen as bodtt ra 9,uadri'lem rna, I '! I' ~I, Hypophysis ' Pons: (anterior and posterior) tobes,/ '/"t. 4th Ventricle,/,...,)./ Choroid plexus'/,,..,, :'",,', " Medu < Fro Mid-sagittal section tluough brain of man (eerebml hemispheres are not shown). (B y John P. Trainor.) two pairs of elevations. The posterior pair is the more prominent. The single pineal body lies in the median line directly anterior to the anterior air of corpora quadrigemina. Under the cerebellum and caudad to it lies the medulla oblongata. The membranous roof of the medulla is often removed with the bony covering, or it may be collapsed to expose the fourth ventricle of the brain. Ventral surface. A conspicuous landmark on the ventral surface of the diencephalon is the optic chiasma produced by the entrance of the optic nerves. Each optic nerve sends part of its fibers to the side of the brain opposite that of its retinal connections. The optic chiasma is the "crossing over" bridge for these,fibers. The continuation of the nerve from the chiasma into the brain is known as

193 \ THE NERVOUS SYSTEM 189 the optic tract. Directly anterior to the chiasma is the anterior perforated space, lateral to which are the olfactory tracts of the qerebrum. These spread as they pass posteriorly from the olfactory lobes. The tracts may be distinguished by slight differences in coloration and indentation. They extend to the medial rounded edge of the cerebrum at a region known as the hippocampus. Within the posterior curvature formed by the optic chiasma and tracts is the pituitary body.. This is attached to a slight rounded elevation, the tuber cinereum. When the stalk of the pituitary is Moss~ intermedib - Arlterior ;_ commisure Pineal bod~. Corpora'1.uadriCjemind //;" Ventricle /. / I /, I.Connecfi6n +0 Hypophysis FIG. lo.8.-mid-sagittal section through brain of the cat (cerebral hemispheres not shown). (By John F. Trainor.) detached from the brain, a slit-like opening appears in the cincreum which is continuous with the third ventricle. Directly caudad to the tuber cinereum is a pair of small rounded mammillary bodies. On either side may be seen processes that tend to unite the cerebellum and cerebrum. These are the anterior extensions of the crura cerebri, which become hidden posteriorly by the pons varolii. The pons appears as a wide band crossing the brain near the forward limits of the cerebellum. It carries fibers that connect the cerebrum and cerebellum with the medulla. The anterior pyramids are caudal extensions of the crura cerebri and appear just posterior to the pons, immediately adjacent to the mid-line. Here occurs a decussation, or c1lossing over, of fibers that pass from the brain to the cord. Lateral to the pyramids anteriorly, the rounded margins

194 190 FUNCTIONAL ANATOMY OF THE MAMMAL of the brain form the trapezoid bodies, which consist of transver~e fibers interrupted by the pyramids in the mid-line area. Caudad to the trapezoid bodies and lateral to the pyramids are the olivary bodies, which are oval-shaped elevations somewhat obscure in the cat. Partly surrounding the olivary bodies are the.. rather inconspicuous restiform bodies, or posterior crura. They are caudolateral connections between the medulla and cerebellum and appear as continuations of the ventral and lateral columns of the spinal cord. The restiform bodies, crura cerebri, and a third paired process, the middle crura, formed by the lateral margins of the pons, make up the three more superficial connecting clements of the longitudinal series of brain divisions. The internal features of the brain. In the median sagittal section of the cerebral hemispheres, cut edges of the corpus callosum are seen as forming the roof of the median communication of the lateral (first and second) ventricles. This large commissure connecting the two cerebral hemispheres spreads internally as corpora radiata in the thick roof of the lateral ventricles. Since such connections consist chiefly of nerve processes, they appear white and more dense in contrast to the gray matter. Below the anterior curve (genu) of the callosum is a ventral fork, the fornix, which is the sharply reflected posterior wall of the median portion of the cerebrum. A prominent rounded massa intermedia appears below and posterior to the fornix, occupying the depressed area that represents a lateral half of the third ventricle. This rounded portion of the diencephalon appears as a dense grayish-white mass crossing the mid-line. Since the fornix above represents the posterior limit of the cerebrum, the massa intermedia represents the medial part of the thalami. N ear the more ventral extension of the fornix is a much smaller transverse bundle of tissue, the anterior commissure, directly in front of the conspicuous massa intermedia of the thalamus. The cut edges of the optic chiasma will be seen at the floor of the region. The principal mass of the diencephalon is seen by gently lifting the cerebral hemisphere where it overlies the other portions of the brain, Each hemisphere covers a rounded elevation of thalamus, which is connected centrally by the more narrow massa intermedia. The thalamus is thus shaped somewhat like a dumbbell with the mass a intermedia as the central handle. The conspicuous enlarge~ ments are lateral thalami, lying immediately craniad and laterad to the corpora quadrigemini.

195 THE NERVOUS SYSTEM 191 } The cerebellum does not contain a cavity and in the sagittal section presents a branching effect of the white matter known as the lp'bol\ vitae. The communications of the ventricles may also be observed in this section if care is taken to locate the exact mid-line. Transverse and frontal sections of the brain expose many more details. The interrelations of the various nerve tracts may be determined by such sections. However, without carrying such a study far beyond the sc~pe of this text, these details are more or less meaningless. Some functions of the brain. In general, the brain is analogous to a complicated s\vitchboard possessing numerous connections with various relay centers and lines of communication. The cerebral cortex has to do with consciousness and the so-called higher faculties which involve initiativeness. The thalami contain important exchange centers connecting the cerebrum with lower divisions of the central nervous system. Anterior corpora quadrigemina form a part of the deep origin of the optic nerves. It is said that the relative size of the anterior corpora are proportionate to the developed use of the eyes, the anterior pair in the mole being rudimentary. The posterior pair is associated with hearing and has developed in connection with the more efficient hearing mechanism of the mammal. The exchange centers of the thalami and corpora quadrigemina also involve nerve tracts of complex character. The midbrain is also associated with "muscle sense," or the activities of skeletal muscles that do not require strict conscious effort through cerebral centers. The cerebellum is especially concerned with equilibrium and muscle coordination in maintaining balance. The control is largely of a reflex character. Because of its equilibrium function, it is also in close communication with the semicircular canals of the internal ear. The medulla contains many of the so-called "lower centers" that are persistently active in the nervous control of essential involuntary activities. Here are the centers that affect respiration, heart beat, and the control of blood flow to areas where it is most needed. These centers are of fundamental importance in merely maintaining life. A cat may live hours or even days without the cerebrum, but any severe injury to the medulla is of serious consequence. For this reason a blow on the back of the head is likely to be much more dangerous than one on the frontal region. These centers in the medulla, however, are greatly influenced through conscious connections. The heart may be seriously affected by a shock of consciousness. Although one may be able to hold one's breath long enough to lose consciousness, respitations begin immediately when the influence of conscious effort is terminated.

196 192 FUNCTIONAL ANATOMY OF THE MAMMAL THE CRANIAL NERVES This portion of the peripheral nervous system is concerned with the nerves that have their superficial origin on the brain and their exits through the cranial foramina.. In the mammal 12 pairs of such nerves are found. Because of the morphological and physiological complexity, early anatomists (and physiologists) were content with numbering them in accordance with their position. Some attempts have been made to indicate the probable relation of cranial nerves to nerves of the cord, but evidences of embryology, as well as of comparative anatomy, tend to complicate any Sl.Iperior rectus muscle tera 1 rectu s 'or rectus Rdentary (medial aspect) FIG. 1O.9.-Distrihution of principal cranial nerves of the cat. The orbit is cut open; the zygomatic arch and part of thc.craniat wall is removed. and the mandible rellected downward to expose its inner surface. Numbers refer to numbers assigned cranial lierve,. (Modified (rom Mivart.) simple homologous features. However, the more posterior cranial nerves do bear certain morphological and physiological resemblances to the adjacent spinal series as the medulla merges into the cord. The principal points of difference presented by the cranial series as compared with the spinal nerves are (1) spatial regularity is not so well exhibited; (2) they arise from a single root; (3) the purely sensory nerves from special sense organs bear no ganglia; (4) they are not all of similar embryonic origin; (5) some are strictly motor, some strictly sensory, and others are mixed with ganglia present for sensory portions of the mixed nerves; (6) the superficial origins are extensive in some cases; (7) only the more caudal of cranial nerves connect to the sympathetic division of the autonomic system.

197 THE NBRVOUS SYSTEM I 193 ~..,... o i:' o en W. 2 o. S <' 0 :c;~ 0." 00

198 194 FUNCTIONAL ANATOMY OF THE MAMMAL

199 THE NERVOUS SYSTEM 195 '1'0 dissect the cranial nerves of a mammal in any detail, several specimens may be needed, and it is not usually attempted in general anatomy courses. For special study, the skull can be partly opened a~d placed in 10 per cent formalin to harden the nerve tissue. After a few days, the bones may be decalcified by leaving the head and neck in about 5 per cent nitric acid for several days and then washing for several hours in running water. This procedure allows one to follow the nerves more easily to their origin, but it is still difficult to study the innervation with accuracy and completeness. A descriptive table precedes for use as a general reference. It should be noted that the superficial origin or attachment of a nerve on the brain does not indicate the position where the cell bodies of the nerves may be located internally. GENERAL FEATURES OF THE SPINAL CORD AND NERVES The cord is an extension of the medulla and has to do with conduction, modification, transfer, and association of nervous impulses as well as the control of certain reflexes. In the extreme caudal region, the cord terminates as a nonnervous filum terminalis. The small central canal extends throughout the cord as a continuation from the fourth ventricle of the brain (see Figs and 10.3). When free of the meninges, \he cord exhibits a deep dorsal and a more shallow ventral fissure, the two incompletely separating it into halves. On either half are two lateral fissures, or furrows, that roughly divide each half into three columns. The dorsal lateral furrow is indistinct but may be seen at the point where the dorsal roots of the spinal nerves join the cord. The more distinct ventral lateral furrow lies at the position of the origin of the ventral roots. Between these furrows is the lateral column of the cord, while above and below are the dorsal and ventral columns, respectively. Some of these points are best seen in a histologic section. In cross section, the centrally located gray matter resembles the form of a short-bodied butterfly with wings extended. The upper lateral extensions are known as the dorsal (posterior) horns, while the lower extensions are the ventral (anterior) horns. These contrast sharply with the surrounding white matter. The superficial origins of the spinal nerves approximate the horns with which they communicate.... Each spinal nerve arises by the two roots, previously mentioned; which may be demonstrated by removing the lamina of the vertebrae. Near the superficial origin of each dorsal root is a gan-

200 196 FUNCTIONAL ANATOMY OF THE MAMMAL glion in which cell bodies relay sensory impulses to the cord- by relatively short axon processes. The ventral roots carry motor fibers away from the cord, and the cell bodies of these neurons lie within the ventral horn of the cord. The motor cell bodies are relatively large and numerous, and smear preparations are easily made for histological study from the ventral root. The spinal cord of the cow, if secured rather fresh from a slaughterhouse, is good material for these preparations. The dorsal root ganglion lies just inside the intervertebral foramen and is protected by the meninges. The two roots immediately unite to form the common spinal nerve. Since the spinal nerves carry both motor and sensory fibers distad to the union, they are mixed nerves (see Fig. 1.2). THE SPINAL NERVES OF THE CAT About 40 pairs of spinal nerves t:ypically occur in the cat, many of which are involved in plexi. The nerves are named in relation to the vertebrae with which they are associated. Since the first cervical nerve finds an exit above the atlas, 8 pairs of cervicals are present (Cl to C8), 13 thoracic (Tl to T13), 7 pairs of lumbar (Ll to L 7), 3 sacral (Sl to S3), while the caudal may be somewhat variable in number in accordance with the number of tail vertebrae. Just distad to the union of the dorsal and ventral roots of each nerve, a small dorsal branch extends to the dorsal musculature and skin. From the ventral surface of the nerve, small twigs are also given off to the sympathetic ganglia. These are known as rami communicantes. The main trunk of the nerve passes ventrally to become more or less widely distributed. Rather distinct plexi are formed by unions of the spinal nerves in the cervical, brachial, lumbar, and sacral regions. Each plexus invqlves the intermingling of nerves to form complications of flbers rather close to their origin from the cord. The extensions from the plexus are much longer than the nerve trunks from the cord to the plexus. The cervical plexus is formed by an interlac~ment of the first four or five cervical nerves. The trunks of these nerves pass from below the anterior portion of the scaleni muscles and below the sternomastoid. The phrenic nerve in the cat is characteristically formed from branches of the fifth and sixth cervicals to pass back to the diaphragm through the thoracic cavity. The brachial plexus observed in the muscle dissection is formed from the sixth, seventh, and eighth cervical, and the first thoracic, to supply the thoracic appendages. The last four

201 THE NERVOUS SYSTEM 197 lumbars form the lumbar plexus, which is closely associated with the sacral plexus since the last two lumbars also communicate with the three sacrals to form the sacral division. The lumbar and sacral are sometimes considered together as the lumbosacral plexus. The nerves that are not involved in plexi (most thoracic and the first few lumbar) are more primitive in character and retain their segmental distribution. The segmental arrangement may be seen by their terminations on the trunk when the skin was removed. Plexi are developed in conformation with the highly developed appendages that call for more than mere segmental innervation. The neck and thorax are ihnervated by less complex nerve associations. The brachial plexus (see Fig. 4.9) If the suggested method of muscle dissection was followed, the brachial plexus became exposed with the transection of the rhomboideus, serratus magnus, and levator scapulae muscles. In the muscles dissection it was suggested that a preliminary examination of nerves be made with the view to studying muscle innervation. If necessary, the muscles of the region. should be reviewed, since the nerves are described chiefly in relation to the muscles innervated. The nerves making up the plexus should be carefully cleared of connective tissue back to their emergence from between the divisions of the scaleni musculature. To observe the dorsal and ventral roots, it is necessary to chip away the neural arches and lamina of the vertebrae. A suitable instrument for this is a small pair of electrician's nippers. The dorsal branches are small and difficult to locate as are the twigs to the sympathetic ganglia which pass ventrally from the spinal nerves. These latter may be picked up later from inside the body cavity and traced back to the spinal nerves. The large ventral divisions of the nerves that contribute to the plexus form a complex of interconnecting branches which is difficult to follow. However, it is possible to determine rather accurately the unions from which the longer extensions arise. These unions which participate in the formation of an extension are somewhat variable, but there is remarkable uniformity in the ultimate nerves that continue from the plexus to innervate both extrinsic and intrinsic musculature of the appendage. Some also send branches to the skin of the region. If we consider t\le phrenic nerve as being outside the brachial plexus, 13 nerves (and their branches) arise from the plexus. Eight

202 198 FUNCTIONAL ANATOMY OF THE MAMMAL nerves of the plexus innervate the shoulder region, and five ext~nd into the forelimb. The following description will be found typical, and variations that may occur may be easily recognized. The nerves are named mostly from their positions. To shoulder region 1. Suprascapular. Most craniad of plexus; chiefly from C6 to penetrate the supraspinatus near the cranial border of the scapula where it divides, one branch going deeply under the acromion process to the infraspinatus muscle. May also give a branch to cla vodel toideus. 2. Anterior subscapular. From C6 and C7; or may have no main trunk but arise as two or three extensions to digitate to the subscapularis muscle which occupies the subscapular fossa. 3. Middle subscapular. From C7 to anterior border of teres major somewhat below the middle; may send branch to teres minor. 4. Posterior subscapular. Arises from C7 and C8; passes directly to the anterior border of the latissimus dorsi where it breaks up into numerous branches. 5. Short anterior thora~ic. Arises from C7 and passes sharply ventrocraniad to middle region of pectoralis major. May be located most easily on the muscle and traced to the plexus. 6. Long anterior thoracic. From C8 and Tl; passes back to pectoralis minor; a short branch usually extends across to the latissimus dorsi. 7. Axillary. Arises chiefly from C7; passes between teres major near its proximal end and the subscapularis, going through the angle formed by the head of the humerus and glenoid portion of scapula (at axilla); gives branches to acromio- and spino-deltoids; and extends a branch to the clavodeltoideus somewhat below the clavicle. 8. Posterior thoracic. Arises from C7 to pass posteriorly and dorsally beneath scaleni to the serratus anterior, near the origin of the third digitation. The nerve is usually flattened and obscured by the fascia where it emerges beneath the scalini to reach the serratus musculature. To arm region 9. Ulnar. The ulnar nerve arises chiefly from TI, passes down the upper arm, following the course of the brachial artery to enter the antibrachium around the elbow at the media:l epicondyle (crazybone nerve). Divides into two branches, one going to flexor carpi

204 200 FUNCTIONAL ANATOMY OF THE MAMMAL other structurally, i.e., do not form plexi. The ventral branches are fela-, tively smaller, and the bulk of each nerve extends along a rib just inside the thorax as an intercostal nerve. These may be observed by tearing away the pleura next to the internal intercostal muscles. They innervate the internal and external intercostals, and each nerve possesses fibers to both inspiratory and expiratory muscles. These act in an alternating rhythmic manner through a control center in the medulla. The respiratory center in the medulla communicates with cell bodies of the cerebral cortex so that conscious change in respiratory rate and amplitude can be made. Since each muscle fiber between the ribs is relatively short, the intercostals are favorite histological material in studying nerve terminations. The lumbar plexus The last four pairs of the seven lumbars are concerned in this plexus. The three lumbar nerves craniad to the plexus pass independently to the skin and muscles of the ventral and lateral abdominal wall. One reason for considering the lumbar plexus separately from the sacral series seems apparent in locating the nerves. Essential features of the plexus are most easily exposed by removing the abdominal viscera and approaching the nerves from the internal aspect of the body,vall. The entire alimentary canal may be freed from the dorsal mesentery and carried forward past the kidneys. The genito-urinary apparatus may be removed, leaving only the vena cava and aorta below the kidneys as landmarks. This dissection exposes the dorsal body wall and brings into view the prominent psoas, or loin, muscles, which lie under the peritoneum of the dorsal body wall. The more prominent in the cat are the iliopsoas and the psoas minor. The iliopsoas is the larger of the two, and its lateral margin lies next to the transversus abdominis. The psoas minor somewhat overlies it and must be separated posteriorly where it tapers considerably as a tendinous structure. Before removing the muscles to locate the plexus proper, the nerves of the plexus should be located and traced in both directions. These nerves will be described in general, the details may be worked out more completely if desired. Lumbar division 1. Genitocrural. Two branches of this nerve may be seen rather easily. A small medial branch may be observed just laterad to the external iliac artery near the bifurcation of the aorta. It follows the iliac artery to the ventral pelvic region. A luteral branch passes along the psoas minor muscle where posteriorly it crosses the ilio-

205 THE NERVOUS SYSTEM 201 psoas. It then passes obliquely through the abdominal wall to the medio-anterior surface of the thigh. The genitocrural arises as an extension of L4. 2. External cutaneous femoris. This nerve is somewhat larger than the genitocrural. It passes between the iliopsoas and psoas minor where it crosses transversely at the level of the iliolumbar artery, which it follows to penetrate the abdominal wall. It is distributed along the anterior margin of the thigh and extends along the integument almost to the knee. It arises from a connecting strand between L4 and L5. 3. Anterior crural. This is the largest of the group. It may be seen under the posterior limits of the iliopsoas in the wall dorsocraniad to the bifurcation of the common iliac veins. At this point branches arise, one of which follows superficially along the femoral artery and vein on the medial surface of the leg as the saphenus nerve. Its cutaneous branches extend to the digits. Other branches innervate the sartorius, vastus medialis, vastus intermedius, and rectus femoris. It arises from L5 and L6. 4. Obturator. This nerve lies just mediad to the anterior crural of which it superficially appears as a branch. It may be readily verified since it passes through the obturator foramen. It innervates the obturator externus, adductor femoris, gracilis, and others and arises from a connection between L6 and L7. The sacral plexus The chief extensions from the sacral plexus are located more dorsally than those of the lumbar. The plexus proper may be uncovered by picking away the musculature over the sacral region and then carefully removing the heavy transverse processes of the adjacent lumbar vertebrae. The dissection of the lumbosacral plexus as a whole requires considerable time and patience. For our purposes the chief nerves of the sacral division will be described so that they may be traced either to the plexus or to their points of distribution, or both. 1. Great sciatic. The great sciatic nerve is by far the largest nerve of the division; in fact, it is the largest of all peripheral nerves. It is exposed with the transection and reflection of the biceps femoris muscle to which it is rather closely applied on its inner surface. The nerve arises chiefly from the seventh lumbar nerve but also receives branches from L6 and 81; in the plexus region it lies ~dorsad and mediad to the -lbturator nerve of the lumbar division. From its origin it passes around the great sciatic notch of the pelvis down the

206 202 FUNCTIONAL ANATOMY OF THE MAMMAL leg, where back of the knee (popliteal space) it divides into an internal and external popliteal nerve. The external branch, also known as the peroneal nerve, further divides into the musculocutaneous, to the peronei musculature and to the dorsal surface of the foot, and the anterior tibial nerve, which supplies the skin; tibialis anterior, etc. The internal popliteal nerve passes posterior to the tibia to form the plantar nerves which reach the digits. There are other minor branches anterior to the popliteal. 2. Lesser sciatic. The lesser sciatic nerve is distributed to the lateral surface of the biceps femoris muscle and in the region of the anus sends branches around the perineum and to the fat around the base of the tail The longest extension is along the lateral surface of the biceps femoris and reaches almost to the popliteal space. It arises from 81 and 82 and usually receives a conspicuous branch from the great sciatic. 3. Posterior hemorrhoidal. This nerve passes along the lateral aspect of the rectum, which it crosses to the urethra and bladder. It arises from 82 and Superior gluteal. This nerve extends over the dorsal border of the ilium between the pyriformis and gluteus medius and is distributed to the gluteus medius, gamellus superior, and gluteus minimus. It arises chiefly from the first sacral. 5. Inferior gluteal. This nerve lies along the dorsal surface of the great sciatic nerve in the pelvic region, which it also leaves at (' the great sciatic notch. It sends branches to the caudofemoralis, gluteus maximus, and pyriformis. It arises from the lumbosacral cord or union in the region of the first sacral Other smaller branches are the pudic nerve, which supplies the genital parts, and certain nerves to the smaller muscles around the anus and root of the tail. The nerves of the tail, or caudal nerves, are similar to the other generalized spinal nerves. They innervate the musculature and skin of the region. With these there are no direct communications to the sympathetic cords. THE AUTONOMIC DIVISION Much of this division has been described in connection with the survey of internal anatomy and in the description of the peripheral division of the nervous system. We may now further amplify previous descriptions and summarize the essential features of involuntary inner~ation.

207 THE NERVOUS SYSTEM 203 'the- cranial portion of the parasympathetics consists of parts of the oculomotor, facial, glossopharyngeal, and vagus nerves. The sacral portion consists of fibers of the sacral spinal nerves. The other set of nerves nqlion nodosum of voqus Voqo-sympathetic trunl. :::r--carotid artery renlc nerve Lobe of lun9 (cut) R. ventricle 1.:. phrenic-i..---'y:::...-.~i n er\ie A~'lt-fl:;"_- 'Pulmonary veins :D._-Sympathetic trunk Splanchnic nerve II-,,-Abdominol sympathetic trun k FIG. lo.lo.-cervical and thoracic nerves of the cat in relation to conspicuous landmarks (left side only is shown). of the autonomic division is the sympathetic, which arises from ganglia receiving impulses from the central nervous system by way of the rami communicantes. Plistganglionic fibers extend from the ganglia to innervate the same structures that are innervated by the parasympathetics.

209 THE NERVOUS SYSTEM 205 thetic division, and the large cervical ganglia represent fusions of the original segmental type. Before reaching the diaphragm, one or two conspicuous splanchnic branches are seen to diverge from the trunk and pass through the diaphragm to a pair of ganglia that lie on the celiac and superior mesenteric arteries. These are named Splanchnic nerve Diaphragm Superior mesenteric artery Adrena I 91and Seqmental9on'llia of Abdomina I sym.pathetic tru nk. Kidney La r~ e -----\"". Intestine +--tl--abdominal aorta ~":::..I-_LGenitol artery Inf mesenteric artery Inf. mesenteric qanqlion :FIll. lo.ll.-lower thoracic and abdominal oyllipathetic nerves of the cat. with reference to the arteries but appear superficially as a single semilunar ganglion. From this ganglion, numerous fibers form a plexus (solar plexus) that innervates the viscera of the region. The sympathetic trunk continues caudad to the caudal region, but only one conspicuous ganglion lies further along its course. This is the inferior mesenteric, which lies on the artery of the same name. Here again a network of fibers extends to the viscera of the lower pelvic region. In general, these fibers innervate the parts supplied by the sacral parasympathetics. Particular functions of these autonomics may be learned from standard texts on physiology.

210 '206 FUNCTIONAL ANATOMY OF THE MAMMAL Discussion. In man and some other mammals, the sympathetic cord and vagus nerve do not combine into a common trunk. Furthermore, the connections of the ganglia with peripheral nerves appear to be somewhat variable. However, the superior cervical ganglion, in mammals generally, communicates with the last three cranial nerves and the first three cervicals. The last five cervical nerves and first three thoracic, in mammals generally, send rami communicantes to the inferior cervical ganglion. The first segmental thoracic sympathetic ganglion, therefore, is found at the level of the fourth thoracic nerve. Confusion in terminology appears in this connection since in the cat, for example, the inferior cervical ganglion is clearly within the thoracic area rather than in the neck. The fusion of thoracic ganglia with lower cervical segmental ganglia has led to the use of the term "stellate ganglion" (star-shaped) to be applied to the ganglion under these conditions. But its application does not appear to be consistent in the literature. In the dog, the stellate ganglion lies somewhat craniad, compared with its position in the cat. The cardiac accelerators in the dog can therefore be reached more easily without so much danger of entering the pleural cavity and causing collapse of the lung in experimental work. This feature is important in experimental physiology, which involves surgical technique on anesthetized animals. One of the most interesting circumstances of the autonomic division is its close functional (physiologic) similarity with certain endocrine organs. Recent investigations have shown that the superior cervical ganglion of the cat, when stimulated through its nervous connections, produces a substance that is similar, if not identical, to adrenalin. For some time, it has also been known that stimulation of the vagus nerve produces a chemical substance (acetylcholine) that causes cardiac inhibition when administered to the heart musculature as a drug and that is antagonized by adrenalin. Thus, we see that nervous stimulation in these cases produces hormone-like substances from sympathetic ganglia and at parasympathetic terminations. Here the basic processes of nervous and chemical regulation appear not to be different or distinct phenomepa. 1

211 Chapter XI SPECIAL SENSORY APPARATUS EACH of the various kinds of sensory end organs is strikingly specific in its sensitivity to stimuli. Thus the retina of the eye is responsive to light; sensory epithelium of the inner ear is responsive to vibrations in the air; nasal epithelium and taste buds are responsive to chemicals; and sensory end organs of the skin and internal areas are each responsive to their particular kind of stimulus. End organs show striking structural specialization in conformation with their type of function. D ~':~;:"!!::\ 0\r: FIG. l1.l-the mechanism for taste in man. A, dorsal surface of tongue; B, two types of taste papillae in section and enlarged; C, relative sensitivity on the tongue for the four tastes; ' D, section of a taste bud enlarged and diagrammatic. (Partly after Parker. From Storer, "General ZoolOGY.") Impulses are transmitted from the terminal receptors to more or less localized conscious centers of the brain. But we do not recognize or perceive these sensations as being within the brain. In the case of the visual sense we have no feeling that an object is photographed in the eye, nor that visual impulses are transmitted to conscious areas. The sensation is projected as at a judged distance from the body. Likewise the sensation or perception of sound is projected at a distance, and we form judgments as to the direction and distance from which the sound waves arose. The olfactory sense is projected to the tongue, smell to nasal epithelium, and touch to the ski,n. We also possess a sense of balance and position that enables us to know the situation and position of the body or of hands 207

212 208 FUNCTIONAL ANATOMY OF THE MAMMAL and feet, and we can make well-directed movements such as feeding ourselves while blindfolded. This curious projection of sensations is well illustrated in cases where feet have been amputated and the subject will olfactory FIG Anatomy of the olfactory sense in man. A, location of the olfactory epithelium in lateral wall of nasal cavity; B, transverse section of cavity; C, enlarged section of olfactory epithelium. (Adapted from Parker. From Storer, "General Zoolo(JY. " ) pressure waves in endolymph stimulate hair cells HI!H iii ill HI II I HI II: III Ii[ Ii! II I III in III U! cochlea (as ifuncoilcdl FIG The mechanism of hearing and equilibrium in mall. A, general structure of the ear; B, c ro~~ section of a part of the cochlear area; C, enlarged section through the spiral organ of Corti showing sensory hair cells; D, diagram of sound transmi~sion from outside air to impulse in auditory nerve. (From Storer, " General Zoology.") experience itching or painful sensations at specific areas of the toes long after the feet have been amputated. Another striking feature of the special sensory mechanism is in the specific character of the sensation regardless of the type of the initiating stimulus. A sharp blow on the head may mechantcally stimulate the retina by jarring it, and we "see stars." A strong flash of light is seen

213 SPECIAL SENSORY APPARATUS 209 when the optic nerve is cut in surgically removing the eye. Pressure stimuli or foreign bodies in the ear may make the "head roar." An even more specific response is exhibited by the end organs of touch. An end Organ specific for cold will produce a sensation of cold even when stimulated by a warm rod. THE FUNCTIONAL ANATOMY OF THE EYE The eye is usually described as being constructed like a camera. Eyes of vertebrate animals in general are fundamentally similar, not only in design but as to the number, character, and innervation of the muscles that move it within the orbital fossa. The fundamental features of the eye and closely associated parts together with nerve and brain connections are more readily dissected in a cartilaginous fish than in the mammal. In forms such as the shark, the nerves can be followed through the brain case by dissecting through the relatively soft cartilage. Eyes of sheep or pigs, which may be obtained fresh from slaughterhouses or as special preparations from supply companies, are generally more suitable for study than eyes from embalmed bodies. Therefore, the descriptions given for the study of the organ as a separate part of anatomy is generalized rather than specifically referable to the cat. Mirror examination of own eye A study of the eye and closely associated structures may well begin with an examination of the superficial characters of your own eye as seen in a mirror. Observe that the upper eyelid extends to the lower margin of the eyebrow and that the lower lid more gradually merges with the skin at the lower rim of the orbital fossa. The lower lid is relatively stationary. With the eye wide open and looking directly ahead, the free margins of upper lid and lower lid are separated from each other by an elliptical gap. The gap is called the palpebral fissur_e. The exposed surface of the eye is kept uniformly moist by frequent blinking. The outer margins of the two lids are joined at inner and outer angles. The inner angle is rounded, and the eyelids here do not press so firmly against the surface of the eyeball. These conditions leave a little lake in which tears collect. In the inner margin of this area (lacus lacrimalis) is a fleshy elevation, the caruncle, best seen when the eye is rotated laterally. A red-colored fold is attached to the outer margin Of the caruncle. The outer fold is the plica semilunaris, which is a vestige of the third eyelid of the cat, most other

214 210 FUNCTIONAL ANATOMY OF THE MAMMAL mammals, and other terrestrial vertebrates. The third eyelid spreads horizontally across the eye and is usually referred to as the nictitating membrane. The caruncle usually appears somewhat\ yellow in color; it possesses modified sebaceous glands associated with extremely fine hairs. When the eyes are wide open and looking straight ahead, the upper and lower lids expose the upper and lower limits of the central pupil and the surrounding pigmented iris. The pupil appears black because it is an aperture into the dark interior of the eyeball and is covered by transparent tissue. The outer tunic or covering of the entire eyeball is called the tunica fibrosa. The portion of the tunic passing over the iris and pupil becomes highly modified as the transparent cornea. It joins the rest of the eyeball at a circular furrow and curves more prominently than does the posterior part of the globe. The junction of the cornea with the rest of the fibrous tunic of the eye consists of a gradual transition of corneal cells into an epithelial covering, the conjunctiva. This consists of several layers of cells that continue over the eyeball, as the scleral conjunctiva, to its attachment with the inner surface of the eyelids, and also continue in a modified condition to form the entire inner surface of the lids. The inner lining of the lid is called the palpebral conjunctiva and is a type of mucous epithelium. The white tissue back of the cornea is the scleral portion of the tunica fibrosa. This is a tough firm connective tissue that gives support and protection to the delicate internal mechanism. The sclera back of the attachments of the inner lining of the lids, of course, does not possess the scleral conjunctiva. When a study is made of the excised eye, these attachments should be located. The free rims of the eyelids are thin at the lateral angle and broaden as the inner, or medial, angle is approached. By pulling the lower lid down and the upper lid upward we can distinguish an outer and inner margin, the lashes occurring on the outer. At the level of the plica semilunaris the rim of each lid possesses a fine opening, the punctum lacrimalis, situated on an elevation, the papilla lacrimale, which appears pale in color. The opening is perhaps most easily seen in the lower lid by drawing the lid down so as to protrude it away from the globe. These openings (upper and lower) lead into lacrimal canals, which eventually drain tears into the nasal region. Tears are formed by lacrimal glands that lie In the upper and lateral portion of the orbital region. The secretion is carried down-

215 SPECIAL SENSORY APPARATUS 211 ward by numerous ducts into the space between the lining of the lids and surface of the eyeball and spreads to the inner angle of the lids. Some accumulates in the lacus lacrimalis to be drained through the punctum lacrimalis. The tears serve to prevent the exposed portions of the eye from drying. Overflow of tears at the rims is largely prevented by oily secretions from a series of small sebaceous glands. The openings of these can usually be seen in a row on the inner surface of the rim. Extrinsic muscles of the eye (see Fig. 10.9) These muscles move the eyeball in the orbit and in man and most vertebrates consist only of two oblique and four recti muscles. In the cat, sheep, and some other mammalian forms an additional muscle occurs which is known as the retractor. When present, the retractor mostly surrounds the optic nerve as a series of slips and functions in keeping the eyeball close within the orbit when the head is bent down. All recti muscles and the superior oblique arise near the optic foramen. The inferior oblique arises from the anterior floor of the orbit. The recti muscles are the medial, lateral, superior, and inferior. They arise close together near the optic foramen and diverge to their insertions on the eyeball to positions from which the names are derived. All the recti group are innervated by the oculomotor nerve, except the lateral rectus which is supplied by the abducens. The oculomotor also supplies the inferior oblique. Only the superior oblique is innervated by the trochlear nerve. The muscle is unique in that its tendon passes through a pulley-like attachment. Internal features of the eye If a section of the sidewall of the eyeball is removed, the wall is seen to consist of three coats: (1) the superficial tunica fibrosa previously described; (2) a middle vascular coat, which forms the black pigmented choroid layer and the iris as a modification; and (3) the lining epithelium, or retina. In the cat, and some other mammals, the choroid coat contains peculiar crystal-bearing cells forming the tapetum, which appears iridescent green in color and produces the peculiar glow of the eye in the dark. The retina in preserved material appears opaque and may be somewhat shrunken away from its choroid base. It extends forward only a little more othan half of the globe and is an expansion of the optic nerve. Near the center of the nerve as it appears to leave the

216 212 FUNCTIONAL ANATOMY OF THE MAMMAL retina is the blind spot, which does not possess retinal cells but'" is quite vascular. The forward margins of the retina attach to a ciliary body, whic,9 in turn is attached to the crystalline lens. In front of the lens is the anterior chamber containing a lymph~like aqueous humor. Back of the lens is the much larger posterior chamber which contains a gelatinous mass, the vitreous body. Thus light entering the cornea passes through four different transparent elements that may affect for gear ~l'",_for distant objects l~ o FIG Mechanism of sight in man. A, median vertical section of the eye; B, enlarged diagram of the structure of the retina; C, changes in shape of the lens (accommodation) to focus on near and far objects; D, manner in which lells serves to form an image on the retina. (A, modified from Dakin.) (From Storer, "General. Zoology.") the course of the rays: the cornea, aqueous humor, crystalline lens, and vitreous body. The lens functions chiefly in accommodation for distance; the cililil'y apparatus controls its curvature. Working with the lens in accommodation is the pupil, the size of which responds to light intensity and proper focus. To demonstrate the effect of reducing the size of the pupil, one can look at a pinhead so close to the eye that it appears blurred. If viewed from the same distance through a small pinhole, much better focus is obtained. The retina acts as a sensitive plate to the light rays that produce chemical changes setting up a flow of impulses through the optic nerve. Not all these impulses reach the conscious centers, and.. unless attention is directed to things they may make no impression on consciousness. The retina is afforded complete rest only in darkness.

217 SPECIAL SENSORY APPARATUS 213 THE HEARING ApPARATUS Dissection of the essential internal parts of the auditory structures r~quires much time, patience, and skill, even when done on large mammals. Detailed examination of the mechanism is usually not attempted in general courses. The following is mostly a generalized description from which observations may be made. The ear is considered as consisting of three divisions: (1) external, (2) middle, and (3) internal. External parts are the expanded portion, or pinna, apparently designed to facilitate picking up sound waves as a megaphone in reverse, and the external auditory meatus, or ear opening. The pinna is of various forms among the different mammals and is generally supported by a well-defined auricular cartilage. Rather specialized hair surrounds and extends partly over the meatus, apparently serving to keep out dust particles and insects. In man, a prominent, firm projection, the tragus, extends partly over the meatus, and a lobule forms the lower portion of the pinna which is devoid of cartilage. When the meatus is explored with a suitable light, it is seen to terminate at a partition, the tympanic membrane. The middle ear extends from this membrane to the petrous bone of the temporal complex. The cavity of the middle ear contains three auditory ossicles that form a bridge from the tympanic membrane to the margin of a lateral opening of the petrous bone, the vestibular fenestra. In a dried skull, two such openings are seen on the lateral aspect of the petrous: the upper vestibular and a lower cochlear fenestra, which in life is covered by a thin membrane. Adjacent to the tympanic membrane is the malleus, next is the incus, and then the stirrup-shaped stapes which joins the petrous. The function of the auditory ossicles is to transmit the vibrations of the diaphragm-like tympanic membrane to the internal ear within the petrous bone. Another feature of the middle ear is the opening of the Eustachian tube which leads to the pharynx and serves to permit the air pressure within the cavity to conform with atmospheric conditions. Dissection of the internal ear is especially difficult since it is entirely enclosed by the dense petrous bone. The parts cannot be well identified without using special methods and reconstructions. The essential part is the membranous labyrinth consisting of semicircular ducts, a cochlea, sacculus, and utriculus. These are housed in a bony labyrinth. The space between the cavitie;~ in the bone and membranous labyrinth is occupied by perilymph. A similar fluid, endolymph, circulates within the membranous walls.

218 214 FUNCTIONAL ANATOMY OF THE MAMMAL The semicircular canals are essentially concerned with equilibrium rather than with hearing. The sensory auditory membrane of the cochlea only is said to function in an auditory capacity. The sacculus and utriculus are associated with the stationary position of the head. As in the dissection Jf cranial nerves and extrinsic muscles of the eye, the fundamental character of the internal ear is best demonstrated in the elasmobranch fish.

219 Qhapter XII THE ENDOCRINE ORGANS ALTHOUGH all the specialized endocrine organs have oeen partly den scribed in the preceding chapters, it seems desirable to consider then1 in a more systematic and detailed manner. Since the different organs of the system are arranged with neither any obvious structural continuity nor any evident functional interrelations, they may be listed merely as they occur spatially from a cranial to caudal position in the body. Classified in this way the system includes (1) pituitary (hypophysis), (2) thyroid, (3) parathyroids, (4) thymus, (5) islands of Langerhans in the pancreas, (6) adrenals, and (7) portions of gonad tissue (ovaries and testes). In addition to these, several other tissues produce substances with effects similar to the secretions of the more conspicuous endocrine organs. All tissues appear to have a share in the general regulation of the body as an integrated whole. The essential functional feature of endocrine organs is in chemical regulation of body activities. Their secretions are effective in remarkably minute concentration and are conspicuously concerned with such fundamentally important functions as growth, differentiation, metabolism, and the differential regulation of the various organs and systems. The active properties of the secretions are known as hormones. Some act as accelerators of activity, while others serve as inhibitors. The secretions are absorbed by the blood, since the endocrines are ductless glands, and the hormones are carried to all parts of the body by general circulation. Many of the hormones are rather specific in action, whereas others produce a widespread response in tissues generally. The pituitary. The gland lies in the pituitary fossa of the basisphenoid bone and is made up mostly of two distinctive parts, anterior and posterior. These are derived differently embryonically and are also histologically different. The anterior pituitary produces a number of distinct hormones, or principles. The more striking of these affect (1) growth, (2) reproduction, and (3) metabolism. The latter action is principally through activation of the thyroid gland. I An excess of the growth hormone appears to be a direct stimulus to general growth and is responsible for gigantism in man. Lack of the hormone results in a type of dwarfishness. The reproductive hormone may have multiple properties,. but the most striking effect on the gonads is to produce ripening of the germ cells. When extremely immature mammals are 215

220 216 FUNCTIONAL ANATOMY OF THE MAMMAL treated with this principle, precocious ripening (maturation) of the ge"m cells is initiated. The metabolic principle acts in an indirect manner. This thyrotrophic hormone stimulates both development and active secretion of the thyroid gland which, in turn, produces an increase in the metabolfc rate, as well as inducing other changes traceable to thyroid activity. Pituiiary orhypophysis (at base of bram) Thyroid ---_ (over trachea) Jo-o'...'--4-IsIets of Iangerhans (in pancreas), Ovaries --.. (in female) FIG Endocrine organs of man shown semidiagrammatically. Although no specifi c hormones are known from the thymus, it is included because of suspected relationships. (From Storer, General Zoolo(JY." ) The posterior pituitary, separated from the anterior, also produces a num~r of effects when an extract is injected into normal animals. But removal of the posterior lobe does not seem to induce any particular ill effects in man. Possibly, other endocrines may be substituted for it in deficiency, but excesses produce changes not compensated for. The crude extract is known as pituitrin. It is particularly effective in intensifying contraction of the uterine muscularis even when given in minute concentration and also induces a sustained constriction of arterioles generally, causing a marked increase in blood pressure. The thyroid gland. The thyroid, in mammals generally, is a bilobect' structure adjacent to the upper portion of the trachel!. Its hormone in a purified form is known as thyroxin, which contains a large proportion of

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