Digestive Tract of Ganges Dolphin, Platanista gangetica*

Transcription

1 Okajimas Fol. anat. jap., 48 : , 1972 Digestive Tract of Ganges Dolphin, Platanista gangetica* II. Small and Large Intestines By Kyozo Takahashi and Fusao Yamasaki Departments of Anatomy and Biology, Sapporo Medical College, Sapporo, Japan With 24 Figures in 6 Plates -Received for Publication, July 28, Introduction Although many reports have been published on the stomach of whales and sea dolphins, descriptions of their intestines are relatively scarce. Especially, reports on the intestines of river dolphins appear sporadically, and even in the extensive study done by Anderson (1879) on Platanista gangetica the description on the intestine is rather short. The reports on the intestine of Platanista published to date are mainly on the length of the intestines (Anderson, 1879 ; Slijper, 1962) and the presence of caecum (Anderson, 1879 ; Weber, 1886 ; Slijper, 1962 ; Duvernog** ; Flower**) but microscopical observations seem to be lacking. This report, in addition to our previous description of the oesophagus and the stomach (Yamasaki and Takahashi, 1971), deals with the macroscopical and light microscopical observations of the intestine of Platanista gangetica, in comparison with those of whales and sea dolphins. Materials and Methods Of the eight Platanista offered for observations of the digestive tract (see Table 1 in our previous paper, 1971) six specimens were used in the study of small and large intestines. As shown in Table 1, three of them (No. 11, 12 and 17) have almost all parts of the * This investigation was supported by a grant from the Education Ministry of Japan, No and was done as a part of systematic studies of Platanista, now being performed by the cooperators of the Cetacean Research Expedition, University of Tokyo (Director : Professor M. Nishiwaki, Ocean Research Institute of University of Tokyo). ** Cited by Weber (1886). 427

2 428 Kyozo Takahashi and Fusao Yamasaki Table 1. Specimens used for examination. intestines. Only specimen No. 21 was offered with complete whole intestines and was mainly examined in situ for the obs'ervation of the relation between intestines and other abdominal organs. In addition, two fetuses of the blue-white dolphin, Stenella caerureoalba (body length 50.0 and 68.0 cm), were observed for comparison. After macroscopical observations, small blocks taken from desired parts of intestines were immersed in fresh fixative for histological examinations. They were embedded in celloidin and paraffin, then sectioned and stained with hematoxylin-eosin and with Azan. Observations SMALL INTESTINE The small intestine of Platanista consists of duodenum, jejunum and ileum., although the borders between them, especially between the latter two, are fairly difficult to determine. The length of the small intestine, from the end of the third compartment (pyloric stomach) to the ileocaecal junction, was approximately 437 cm in specimen No. 11, 510 cm in No. 12, 525 cm in No. 17 and 250 cm in No. 21 (Table 2). Although the diameter of the small intestine is about 0.8 to 1.6 cm at the oral part of jejunum and is about 0.6 to 0.9 cm at the anal part of ileum, it varies from specimen to specimen, and also varies according to the state of contraction. Generally speaking, the diameter of the oral part of the intestine is much larger than that of the anal part. Duodenum: The initial part of the duodenum forms the so-called ampulla* and the succeeding duodenum proper runs caudad and left- * The duodenal ampulla has sometimes been described as a last part of the stomach, but in this paper, the ampulla is treated as a initial part of the small intestine, because there is a remarkable sphincteric structure between the third compartment of the stomach and the ampulla (cf. Yamasaki and Takahashi, 1971) and because such a structure between the ampulla and the duodenum proper cannot be found. The histological structure itself of the ampulla is similar to that of the third compartment of the stomach.

3 Small and large intestines of Ganges dolphin 429 wards around the head of the pancreas. Then it bends slightly upwards, being fixed to the dorsal abdominal wall by a short mesentery until the duodeno-jejunal flexure which is situated near the median line of the dorsal wall. The duodenal ampulla comes next to, and is located caudally from the third compartment of the stomach. It is a funnel-shaped part approximately 2.5 to 3.0 cm in length and about 2 cm in diameter at its _ oral part, which is demarcated from the third compartment by a circumferential shallow groove (Fig. 1). The ampulla gradually becomes thinner and its anal end continues to the duodenum proper, being demarcated by a shallow depression, but there is no sphincteric structure at this part. In the case of specimen No 11, as shown in Fig. 2, the ampulla is bulbously enlarged, being about 2.5 cm in diameter, and a small, protruding orifice, 0.5 mm in diameter can be seen between the ampulla and the duodenum proper. In this case the inner surface of the ampulla was stained green with bile. The thickness of the wall of the ampulla is almost identical to that of the third compartment (Fig. 2). The inner surface of the ampulla. is smooth, having no circular plicae andwhich are both prominent in duodenum proper (Figs. 2 and 3). Microscopically, the inner surface of the duodenal ampulla is lined with simple columnar epithelium and numerous deep pits were observed (Fig. 4). These pits continue to the branched tubulo-alveolar glands situated in the lamina propria mucosae. The glandular epithelium consists of one kind of cells and the Brunner's gland cannot be seen either in the submucosa or in the lamina propria mucosae. Thus, the microscopical structures of the duodenal ampulla are very similar to that of the third compartment of the stomach. The smooth muscles of the lamina muscularis mucosae are scattered and the lymphatic nodules were frequently observed in the lamina propria mucosae (Fig. 4). In the duodenum proper the villi appear, and the glandulae intestinales are tubulo-alveolar in nature (Fig. 5). It is a very striking feature that no goblet cells were observed among the intestinal glands and also that no Brunner's gland can be seen in the submucosa (Fig. 5). The muscularis consists of inner circular and outer longitudinal layers of smooth muscles. Hepato-pancreatic duct: The ductus hepato-pancreaticus, after receiving several pancreatic ducts, perforates the duodenal wall obliquely (Fig. 6) and a distinct plica longitudinalis duodeni was observed on the inner surface of the duodenum (Fig. 3). The papilla duodeni is remarkable, about 6 mm in diameter, and located 1.5 cm away from the commencement of the duodenum proper. The lumen of the duct which passes through the duodenal wall is enlarged and forms the.

4 430 Kyozo Takahashi and Fusao Yamasaki so-called intramural cystic gland ' found in some species of the whalebone whale and the toothed whale (Kamiya, 1962), and the epithelial structure is microscopically similar to that of the duodenum proper in Platanista (Fig. 6). A precise description of the bile passages, together with that of the liver, will be published in a succeeding paper. Jejunum and ileum: These are suspended by a broad mesentery which arises from the radix mesenterii attached to the median line of the dorsal abdominal wall behind the stomach, and thus the jejuno- Heal loop is very mobile. The length of the radix could not be measured in our cases No. 11, 12 and 17 but it was about 3 cm in specimen No. 21. Well-developed circular plicae can be seen on the inner surface of the jejunum (Fig. 7) and of the oral greater part of the ileum (Fig. 8), but they become gradually irregular and scarce, and the inner surface of the small intestine becomes flat and smooth in the last ca. 50 cm of the ileum (Fig. 9). A distinct longitudinal fold (two folds in the case of specimen No. 21), about 30 cm long, was found at the last part of the ileum (Figs. 12 and 13), almost reaching the ileocaecal valve. It had no relation to the attachmentline of the mesentery. Macroscopically, numerous small spots were seen at the inner surface of the last part of the ileum, especially predominantly near the ileocaecal valve (Figs. 12 and 14). These were well-developed lymphatic nodules in the lamina propria mucosae.(figs. 13 and 14). The villi of the jejunum and the ileum are well shown in Figs. 10 and 11 and those of the former are much longer than those of the latter. The intestinal glands are densely packed, simple tubular ones, and again no memorable goblet cells can be found among them. The muscularis is, as seen in Fig. 13, composed of thick inner circular and thin outer longitudinal layers. Ileocaecal junction and ileocaecal orifice: The ileocaecal junction is located nearly behind the third compartment of the stomach and just caudally and slightly right of the radix mesenterii of the small intestine. The ileum joins the large intestine from the right.side of the abdominal cavity (Fig. 16). There are several blocks of lymphatic tissues, about 1 cm in diameter, in the neighborhood of the ileocaecal junction embedded in the mesentery (Figs. 16 and 17). The ileocaecal orifice is round in shape, about 0.7 cm in diameter, when viewed from the caecal interior (Fig. 14). In specimen No. 11, a prominent Up was observed in the upper two-thirds of the orifice (Fig. 15) and in No. 12 a circular lip was observed around the orifice (Fig. 14). Although these lips were considered macroscopically as the ileocaecal valve, they have no developed circular smooth muscles

5 Small and large intestines of Ganges dolphin 431. inside so that the lips themselves may have no sphincteric function. Instead, the smooth muscles of the ileum and the large intestine join together at the end of the ileum (Fig. 15) and they probably have a function as a ileocaecal valve. Lymphatic nodules were also found in the ileocaecal lip. LARGE INTESTINE The large intestine of Plataivista consists of caecum, colon and rectum. The length of the large intestine (except for the caecum) was measurable in specimen No. 21, but those of other three (No. 11, 12 and 17) could not be measured, because they had no complete large intestines. However, the length of the large intestine was surmised, based on the available data, to be about 40 cm in specimen No. 11 and 12 and about 48 cm in No. 17 (Table 2). Caecum: At the point where the small and large intestines join, there is a distinct caecum (Figs. 16 and 17). It is a pear-shaped blind sac and is 4 cm in specimen No. 11 and 4.5 cm in No. 12 in depth and the maximum diameter is about 3.5 cm in both specimens. The caecal apex is spherical and there is no vermiform appendix at its tip. Mesocaecum can be seen at the upper half of the caecum (Fig. 17). The caecal wall is so thin, 1 to 1.5 mm in thickness, that the green-grayish muddy contents were faintly visible through the wall. The mucosa of the caecum has no villi and the crypti intestinales show some tortuous courses. Colon: The initial part of the colon is funnel-shaped, continuing from the caecum (Fig. 16). At the level of the ileocaecal junction it has a diameter of about 2 cm and the diameter reduces to about 1.2 cm at 3.5 cm away from the ileocaecal junction. In the case of specimen No. 12 the colon reduced its diameter abruptly at 4.5 cm away from the ileocaecal junction. The ascending part of the colon is about 5 cm long and has a mesocolon about 8 mm wide. Then, the colon flexes and runs downwards along the median line of the dorsal abdominal wall. Thus there is no definite transverse portion of the colon as Ohe (1951) noted in the Sei whales. The mesocolon of the descending part is short, being about 5 mm wide. The terminal portion of the colon, which has a 1.5 cm wide mesocolon, shows a tortuous course over 3 cm and continues to the rectum. The wall of the initial part of the colon is thin and its inner surface is smooth as in the caecum (Fig. 18). Several longitudinal folds begin from the thin portion of the colon over ca. 3 cm (Fig. 18). The teniae coli and plicae semilunares are not present in the colon or in the caecum, even microscopically, so that the haustrae coli cannot be found (Fig. 16). The light microscopical structure of the colon is almost the same as that of the caecum (Fig. 20). Rectum and anus : The rectum runs straight, continuing from

6 432 Kyozo Takahashi and Fusao Yamasaki the colon, and leads to the anal orifice. The abdominal cavity reaches very deeply near the anal orifice. On the inner surface of the rectum there are many longitudinal folds which begin at the flexed part of the colon and the linear epithelial transition between the rectum and the anus* (from the anal orifice to the epithelial transition) was distinctly observed (Figs. 21 and 23). As the oral end of the anus (site of epithelial transition) is located about 1 cm in the abdominal cavity, the length of the rectum is very short, being 3 cm in specimen No. 17. The anus becomes wider after recto-anal epithelial transition. The crypti intestinales of the rectum attain a greater length than the caecum and the colon. They differ from the rest of the intestines in the abundance of goblet cells (Fig. 22). The anal epithelium is non-keratinized stratified squamous (Fig. 23) and is remarkably pigmented continuing from the external skin (Fig. 24) but is speckled near the recto-anal epithelial transition (Fig. 21). Discussion It is well known that the initial part of the duodenum of most kinds of cetaceans is dilated and forms an ampulla. This duodenal ampulla has been counted as the last compartment of the stomach by some investigators. In our previous paper, however, the duodenal ampulla of Platanista was excluded from the category of the stomach, based on the facts presented in the footnote on page 428. Anderson (1879) divided the stomach of Platanista into three cavities the first, the second and the third, and he also used the term fourth cavity for the duodenal ampulla in his Plate XXVI, Fig. 1. And he stated, without histological description, that the fourth cavity was not a true gastric chamber, but an enlargement of the upper part of the duodenum. In fact, the histological structure itself of the ampulla, as has already been mentioned, is very similar to that of the pyloric stomach (Fig. 4). The duodenal ampulla of Platanista is a funnel-shaped part, and has a diameter of about 2 cm at the thickest oral part. Its size is far smaller than that of the pyloric stomach (3rd compartment), according to our observation. On the other hand, the diameter of the duodenal ampulla is greater than that of the tubular pyloric stomach in Stenella styx (Gihr and Pilleri, 1969) and in Stenella caeruleoalba, accordin g to our observation. In the case of specimen No. 11 of Platanista this part was observed as spherical and its inner * The part, corresponding to the 'zona haemorrhoidalis' in human, is very long and 4.3 and about 7 cm in specimen No. 21 and 17, respectively.

7 Small and large intestines of Ganges dolphin 433 surface was strongly stained green by bile. Because Platanista has no gall bladder as other cetaceans there is a possibility that the bile might be deposited in duodenal ampulla as well as in the dilated portion of the last part of the hepato-pancreatic duct without backflow to the third compartment. Although Anderson (1879) described that the inside of the sac (= duodenal ampulla) was marked by strong longitudinal folds with no trace of transverse ones, it was flat and smooth in our specimens. Also, he noticed succeeding short, slightly smaller sac, but we could not find such a sac at this part of the duodenum in all specimens examined. Circular folds begin at the duodenum proper and they become gradually irregular in arrangement and become scarce at the anal part of the ileum. The inner surface of the last ca. 50 cm of the ileum becomes smooth and flat (Fig. 9). Although Anderson (1879) noticed that the transverse folds of Platanista were placed somewhat obliquely so that the tract is spiral, and although it is said that the folds spiral in sperm whales (Hosokawa, 1949), the circular folds of Platanista we observed were almost transverse to the long axis of the intestine (Figs. 7 and 8) and if they were spiral the pitch was very small. On the inner surface of the last part of the ileum a remarkable uninterrupted longitudinal fold, about 30 cm long, can be seen (Fig. 12), although Anderson (1879) noticed only short patches of longitudinal folds, about 2 inches long, at this part. The wall of this fold and the neighboring wall of the ileum have many well-developed lymphatic nodules (Fig. 13). The lymphatic nodules increase in number as a result of the presence of this fold at the last portion of the ileum. If the lymphatic nodules develop so markedly in other river dolphins also at this part, they, together with the blocks of lymphatic tissue at the ileocaecal junction already mentioned, may have a close relationship with their food habits or may have a correlation with the immune function recently being discussed. No Brunner's gland can be seen at the duodenum in Platanista. Since Brunner's gland does not exist in some of the cetaceans (Yoshikawa, 1944) and since fish generally have no Brunner's gland, it is suggested that there might be some correlation with living in the water or that the gland might have retrogressed with age, and thus it may require precise inspection of materials in a very early stage of development. The functional relationship between the Brunner's gland and the ' intramural cystic gland at the terminal portion of the bile passages will be discussed in a succeeding paper. As already described, the goblet cells in the intestinal epithelium of Platanista are very scarce in both the small and the large

8 434 Kyozo Takahashi and Fusao Yamasaki intestines, but are abundant only in the rectum (Fig. 22). According to the descriptions of some authors (e. g., Yoshikawa, 1944 ; Harrison et al., 1967), the intestinal glands of the small and the large intestines of cetaceans contain many goblet cells. Our observation seems in accordance to some degree with the Hosokawa's observation in.which he stated that the goblet cells are not so numerous in the small intestine but are rich in the large intestine in Balaenoptera borealis.. The very scarce distribution of goblet cells in Platanista seems peculiar among the animal kingdom. At the juncture where the ileum and the colon join, a distinct caecum which has already been described by Anderson (1879) and others can be seen. In this respect, Platanista differ from other toothed whales which have no caecum. It is a pear-shaped sac (Figs. 16 and 17), and was 4 and 4.5 cm in depth in specimens No. 11 and 12 and was said to be 5 to 8.8 cm (2 to 3.5 inches) in adults by Anderson (1879). According to Hosokawa (1949) and Slijper (1962), baleen whales have a very short caecum, except in the case of black right whales (Omura et al., 1969). The stomach of the baleen whale which has caecum is less complicated in its division than the toothed whale which has no caecum (Hosokawa, 1949). The fact that the stomach of Platanista seems more simple than those of other sea dolphins (Yamasaki and Takahashi, 1971) may have some relation to the presence of the caecum. The description on teniae- and haustrae coli of cetaceans seems to be very scarce. The only report that the authors noticed on this subject was Yoshikawa's (1944), in which he described teniae that consisted of three longitudinal muscular bands in Balaenoptera musculus. In Platanista, teniae were not observed on the caecum and the colon macroscopically, and even in the microscopical observation no sign of teniae could be seen. Although the function of the teniae coli has not been completely understood the presence and absence, of teniae should be clarified in terms of their function on the intestinal movement. As the length of the intestine varies remarkably when measured in a living or in a fixed, contracted state, it is difficult to describe the so-called real length According to the description by Anderson (1879), in Platanista, the length of the small intestine varies from 24 feet 1 inch (745 cm) to 22 feet 2 inches (665 cm) in specimens measuring from 6 to 5 1/2 feet (180 to 165 cm) and that of the large intestine of adult is 2 feet (60 cm) long. In our cases, the length of the small int6gtine and the large intestine (from the tip of the caecum to the anal orifice) was measured in fixed specimens and the results are shown in Table 2. The ratio of the intestinal length to the body

9 Small and large intestines of Ganges dolphin 435 Table 2. Length of the intestines of Platanista (cm) and the ratio of the intestinal length to the body length. * The specimens were incomplete and the values were surmised, based on the available information. length is 4.3 to 4.9 in Platanista in our specimens (No. 11, 12 and 17) and seems generally less than 5. Although it is unclear that the estimation was done in living state or in fixed materials, the ratio in adult Platanista by Anderson (1879) is about 4.3 and seems in accordance with our data. According to the observation by Hosokawa (1949), the ratio is 4 to 8 in baleen whales, and in toothed whales the intestine are longer than the former. The ratio is 11.4 (Cuvier*) or 12 (Rapp*) in Phocaena communis and 12 to 15 in Delphinus delphis (Rapp*). Thus the intestine of Platanista seems shorter than those of most baleen whales and seems markedly shorter than those of sea dolphins. As it is generally said that the smaller the cetaceans, the greater the percentage length of its intestine (Slijper, 1962), the short intestine in Platanista is very characteristic and probably must be interpreted from the viewpoint of food habit and their living environment in fresh water. As for the ratio of the intestinal length to the body length Omura et al. (1969) stated that the length of the intestine of black right whale does not increase greatly after a very young stage, and thus the ratio decreases with age. While in Platanista, as was shown in Table 2, the length of the intestine increases with age judging from the data of a young specimen (No. 21) and others, and also the ratio seems to increase with age up to about 5 in full grown animals. The mesentery in a broad sense of Platanista is characteristic as compared with other mammals in respect to its existence at the anal part of the duodenum (mesoduodenum) and at the whole large intestine (mesocolon and mesorectum) in the abdominal cavity. The breadth of the mesentery is short at the duodenum and colon, but very broad at the jejunum and the ileum. These characteristics of the mesentery of Platanista are very similar to those of baleen whales (fetuses of Balaenoptera physalus and B. musculus) observed by Hoso-. Cited by Weber (1886).

10 436 Kyoz Takahashi and Fusao Yamasaki kawa (1949). According to our observation in sea dolphins (fetuses of Stenella caerureoalba) and to Hosokawa's description in toothed whales (Physeter catodon), the whole intestine, from the duodenum to the rectum, is suspended by a broad mesentery which Hosokawa (1949) proposed calling the mesenterium communa,e In Platanista, as the mesentery is very short at the duodenum and the colon, only the jejuno-ileal loop is very mobile, being suspended by a broad mesentery which originates from the short mesenterial radix. The intestine of Platanista is very unique and is very similar to those of baleen whales in respect to several characteristics described above ; small ratio of the intestinal length to the body length, existence of caecum and the spanning state of the mesentery. According to Hosokawa's consideration, the initial parts of the digestive tract such as the oesophagus and the stomach of animals might be adaptable to food habits, while the intestine will not be affected so much by diet but keeps its original form. If these speculations were acceptable, the structure of the digestive tract is one of the important factors to study in determining the phylogenetical status of Platanista among cetaceans. Summary The small and the large intestines of six Platanista whose body length ranged from 76 to 127 cm were observed macro- and light microscopically and the following results were obtained. The duodenum consists of a funnel-shaped duodenal ampulla and duodenum proper with no sphincter between them. The hepatopancreatic duct opens into the duodenum proper and the duodenal ampulla may deposit secreted bile. The inner surface of the ampulla is smooth, devoid of circular plicae. The Brunner's gland cannot be seen in any part of the duodenum. The circular plicae which begin at the duodenum proper almost disappear at the last ca. 50 cm of the ileum. Instead, a distinct longitudinal fold, ca 30 cm long, was observed at the last part of the ileum. The lamina propria mucosae of this fold and its neighboring wall of the ileum contain many well-developed lymphatic nodules. A distinct caecum was found at the juncture between the ileum and the colon. The colon has no memorable transverse portion and continues to the short,rectum. No signs of teniae and haustrae were found on the caecum and the colon. The anus, from the anal orifice to the recto-anal epithelial transition, is very long. The goblet cells are very scarce in the small and the large

11 Small and large intestines of Ganges dolphin 437 intestines, except for the rectum. The ratio of the whole length of the intestine to the body length is 4.3 to 4.9 in our specimens, and is smaller than those of most baleen whales and markedly smaller than those of other sea dolphins. The length of the intestine increases with age and the ratio seems increase to about 5 in Platanista. The relation of the mesentery to the intestine is similar to that of baleen whales ; the anal half of the duodenum proper has a short mesoduodenum and both the jejunum and the ileum are suspended by a broad mesentery which originates from the radix mesenterii placed behind the second compartment of the stomach. The descending colon is fixed along the median line of the dorsal abdominal wall by a short mesocolon. The intestine of Platanista gangetica is very similar to those of baleen whales in respect to the shortness of the intestine in relation to body length, the existence of caecum and the state of mesentery. The relationship between the morphological characteristics of the digestive tract and the food habit was discussed. Acknowledgement The authors are greatly indebted to Dr. T. Kamiya, Department of Anatomy of University of Tokyo, for his valuable advice and to Mr. A. Mori, Department of Anatomy of Sapporo Medical College, for his skillful technical assistance. References. Anderson, J. (1879). Anatomical and zoological researches : comprising on account of the zoological results of the two expeditions to Western Yunnan 1868 and 1875; and a monograph of the two cetacean genera, Platanista and Orcella. 2 vols. B. Quaritch, London. Gihr, M. and G. Pilleri (1969). On the anatomy and biometry of Stenella styx GRAY and Delphinus delphis L. (Cetacea, Delphinidae) of the Western Mediterranean. Investigations on cetacea. Vol. I. Edited by G. Pilleri. Benteli AG, Berne- Biimpliz. Harrison, R. J., F. R. Johnson and R.S. Tedder (1967). Underwater feeding, the stomach and intestine of some delphinids. J. Anat. (Lond.) 101 : Hosokawa, H. (1949). Some observations on the cetacean digestive tract (in Japanese without English summary). Geiken Hokoku, temporarily printed. Kamiya, T. (1962). On the "intramural cystic gland" of the cetacea (in Japanese with English summary). Acta Anat. Nippon. 37 : Ohe, T. (1951). Iconography on the abdominal cavity and viscera of the Balaenoptera, with special remarks upon the peritoneal coverings. Sci. Repts. Whales Inst. 5: Omura, H., S. Ohsurni, T. Nemoto, K. Nasu and T. Kasuya (1969). Black right whales

12 438 Kyozo Takahashi and Fusao Yamasaki in the North Pacific. Sci. Repts. Whales Res. Inst. 21 : Slijper, E. J. (1962). Whales. Hutchinson, London. Yamasaki, F. and K. Takahashi (1971). Digestive tract of Ganges dolphin, Platanista gangetica. I. Oesophagus and stomach. Okajimas Fol. anat. jap. 48: Yoshikawa, T. (1944). Histological studies of cetacean viscera. III. On the small and large intestines of Balaenoptera musculus, B. borealis, Physeter macrocephalus and Delphinus delphis (in Japanese without English summary). Hokuetsu Igakkai Zassi 59 : Weber, M. (1886). Studien iiber Saugethiere. Ein Beitrag zur Frage nach dem Ursprung der Cetaceen. Gustav Fischer. Jena.

13 Small and large intestines of Ganges dolphin 439 PLATES

14 440 Explanation of Figures Plate I Fig. 1. Ventro-caudal view of the initial part of duodenum and its heighborhood. Lir-right lobe of the liver ; III-3rd compartment of the stomach; Da-duodenal ampulla; Dp-duodenum proper ; Je-jejunum ; Pa-pancreas; Oma-omentum majus. Specimen No. 11. x 1 Fig. 2. Longitudinal section of the initial part of the duodenum. The bulbous duodenal ampulla (stained with bile) and a prominent papilla duodeni (arrow) are well shown. III-3rd compartment ; Da-duodenal ampulla ; Pa-pancreas ; Hp-hepato-pancreatic duct. Specimen No. 11. x 1.6 Fig. 3. Inner view of the ampulla duodeni and the initial part of the duodenum proper. Plica longitudinalis duodeni and plicae circulares are observed. There is no sphincteric structure between the ampulla and the duodenum proper (arrows). Da-duodenal ampulla; Dp-duodenum proper ; Pl-plica longitudinalis duodeni. Specimen No. 12. x1.3

15 441 Plate I K. Takahashi and F. Yamasaki

16 442 Plate II Fig. 4. A photomicrograph of the mucosa of the duodenal ampulla. The pits are deep and the glandular epithelium consists of one kind of cells. Ln-lymphatic nodules. H-E stain. x 80 Fig. A photomicrograph of the wall of the duodenum proper. A transverse section of one of the circular plicae is shown in the center of the micrograph. The structures of the villi and the glandulae intestinales are typically shown. No Brunner's glands were observed in the submucosa. Vi-villi intestinales; Gi-gll. intestinales ; Ts-tela submocosa. H-E stain. x 26 Fig. 6. Longitudinal section of the terminal part of the hepato-pancreatic duct. The part which passes obliquely through the duodenal wall is dilated and the microscopic structures are similar to those of the duodenum proper. Hphepato-pancreatic duct; duodeni; Tm-tunica muscularis; Dl-duodenal lumen. H-E stain. x5 Fig. 7. Inner surface of the jejunum. Plicae circulares are well-developed and extend about two-thirds of the circumference of the lumen. Specimen No. 12. x1.5

17 443 Plate II K. Takahashi and F. Yamasaki

18 444 Plate III Fig. 8. Inner surface of the middle part of the ileum. Plicae circulares are still dominant and run almost transversely. Specimen No. 12. x1.8 Fig. 9. Inner surface of the anal part of the ileum (40 cm away from the ileocaecal junction). The circular folds are almost diminished and the inner surface becomes smooth. Specimen No. 12. x1.6 Fig. 10. A photomicrograph of the mucosa of the jejunum. Villi intestinales and straight glandulae intestinales are clearly shown. Goblet cells are hardly observable. Vi-villi intestinales; intestinales. H-E stain. x 65 Fig. 11. A photomicrograph of the mucosa of the ileum. The length of the villi is reduced as compared with the jejunum.

19 445 Plate Ili K. Takahashi and F. Yamasaki

20 446 Plate IV Fig. 12. Inner surface of the terminal portion of the ileum. A longitudinal fold and the spotted area that consist of lymphatic nodules are shown. Inner surface of the caecal wall and the wall of the colon of this part are extremly smooth. Ileocaecal valve is indicated by arrows. Lf-longitudinal fold ; Caw-caecal wall ; Cow-wall of the colon. Specimen No. 12. x 1.5 Fig. 13. Cross section of the terminal part of the ileum. A prominent longitudinal fold and well-developed lymphatic nodules in the lamina propria mucosae are visible. The inner muscular layer is far thicker than the outer one. H-E stain. x6.7 Fig. 14. Ileocaecal orifice viewed from the large intestine. Specimen No. 12. x 3 Fig. 15. Longitudinal section of the end of the ileum. This section was made from specimen No. 11 of Fig. 18. Note the well-developed lymphatic nodules in the thick lamina propria mucosae. Lp-lip of the ileocaecal orifice ; Ll-lumen of the large intestine ; Caw-caecal wall ; Cow-wall of the colon. x 5.5

21 447 Plate N K. Takahashi and F. Yamasaki.

22 448 Plate V Fig. 16. Ventral view of the caecum and its neighborhood. Note the prominent pearshaped caecum and the several blocks of lymphatic tissue which are embedded in the mesentery. Ca-caecum ; Ie-ileum ; Co-colon ; Lb-block of the lymphatic tissue. Specimen No. 11. x0.6 Fig. 17. Dorsal view of the caecum and its neighborhood. Ca-caecum ; Co-colon ; Ie-ileum ; Lb-block of the lymphatic tissue ; Me-mesentery. Specimen No. 11. x0.7 Fig. 18. Inner surface of the caecum and the colon. The ileocaecal orifice is indicated by an arrow. The inner surface of the caecum and the initial several centimeters of the colon are smooth. The colon reduces its diameter gradually and the longitudinal folds appear at this part. Caw-caecal wall ; Cow-wall of the colon. Specimen No. 11. x 1.6

23 449 Plate V K. Takahashi and F. Yamasaki

24 450 Plate VI Fig. 19. A photomicrograph of the mucosa of the caecum. The crypti show some tortuous courses and the goblet cells are very scarcely observed. H-E stain. x150 Fig. 20. A photomicrograph of the mucosa of the colon. The structure of the mucosa is almost the same as that of the caecum. H-E stain. x 150 Fig. 21. Part of the recto-anal epithelial transition. Note the convoluted and partly pigmented zona haemorrhoidalis. The transition is indicated by arrows. Ac-columnae anales ; As-sinus anales. Specimen NO. 17. x 3.3 Fig. 22. A photomicrograph of the mucosa of the rectum. The length of the crypti intestinales is large and number of goblet cells were observed, especially in the lower half of the crypti. H-E stain. x,60 Fig. 23. A photomicrograph of the retto-anal epithelial transition (arrow). Nonkeratinized stratified squamous epithelium of the anus and the mucosa of the rectum are seen. Rm-rectal mucosa ; Am-anal mucosa. H-E stain. x 25 Fig. 24. Cross section of the upper part of the anus. The epithelium is remarkably pigmented and microscopically the muscularis in this region consists of inner circular and outer longitudinal smooth muscle layers. Specimen No. 21. x7

25 451 Plate VI K. Takahashi and F. Yamasaki