Tympanic Bulla Temporal Bone. Digastric Muscle. Masseter Muscle

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1 Superior view Hyoid Bone The hyoid bone does not articulate with any other bones. It is held in place by ligaments to the styloid process of the temporal bone and the thyroid cartilage of the larynx. It also has muscle attachments. In spite of the fact that it is not attached to the skull, it is considered part of the axial skeleton, specifically part of the skull. It has a shape similar to the mandible, suggesting a common origin. Functionally it is important because it is the origin of muscles that move the larynx during the act of swallowing. Tympanic Bulla Temporal Bone Ventrolateral view, right side The tympanic bulla is hollow and houses the middle ear. The external acoustic meatus opens on its lateral surface. It is part of the temporal bone. Digastric Muscle origin: mandible and mastoid process of temporal bone insertion: by connective tissue loop to hyoid bone nerve: mandibular (V3) and facial (VII) action: elevate hyoid bone, open mouth and depress mandible Masseter Muscle Ventrolateral view, left side origin: zygomatic arch and zygomatic bone insertion: angle and ramus of mandible nerve: mandibular (V3) action: prime elevator of mandible (closes mouth)

2 Facial Nerves (Dorsal and Ventral) VII Ventrolateral view, left side (dorsal facial nerve (VII)) Ventrolateral view, left side (ventral facial nerve (VII)) The facial nerve is cranial nerve VII. It is both motor and sensory. It also has parasympathetic functions controlling the lacrimal gland, as well as the mandibular and sublingual salivary glands. It exits from the skull via the stylomastoid foramen. We will observe this nerve on the lateral portion of the face where the two branches bracket the masseter muscle. We will learn more about this nerve when we study the cranial nerves.

3 Hypoglossal (XII) Nerve The hypoglossal nerve is cranial nerve XII. It is a motor nerve serving the muscles of tongue. It exits the skull via the hypoglossal canal. It runs with the lingual (sublingual) artery medial to the digastric muscle. As with the facial nerve, we will learn more about this nerve when we study the cranial nerves. Phrenic Nerve The phrenic nerve is formed in humans from the union of branches of the anterior rami of cervical spinal nerves 3, 4, and 5. It serves the diaphragm. Remember the mnemonic: "C3, 4, 5 - stay alive - phrenic, phrenic, phrenic!" Although the picture on the left above is not very clear, I left it in to help with orientation.

4 Spinal Accessory Nerve (XI) The spinal accessory nerve is cranial nerve XI. It is a motor nerve that serves the sternocleidomastoid and the trapezius muscles in humans. In the cat it appears along with the hypoglossal and vagus nerves lateral to the larynx and deep to the mandibular lymph node. From here it passes to the deep side of the cleidomastoid muscle. Sympathetic Trunk The sympathetic trunk runs along each side of the vertebral column. It receives neurons from anterior rami of the spinal nerves via the sympathetic trunk ganglia. It serves many organs from the head to the pelvis. It first appears in the cranial end of the thoracic cavity. These pictures show where it first separates from the vagus nerve. Although the picture on the left does not show it clearly, I left it in for purposes of orientation.

5 Vagosympathetic Trunk The vagosympathetic trunk runs along each side of the trachea in the carotid sheath, which also includes the common carotid artery and the internal jugular vein. It is formed where the vagus nerve and sympathetic trunk run adjacent to each other. They do not actually become one structure, and can be separated with a probe. PLEASE DO NOT SEPARATE THEM! Vagus (X) Nerve The vagus nerve is cranial nerve X. It is the only cranial nerve to pass into the body cavities below the neck. It is primarily parasympathetic in nature and is the major nerve affecting the heart and most of the gastrointestinal tract. In the cat it appears along with the hypoglossal and spinal accessory nerves lateral to the larynx and deep to the mandibular lymph node. From here it runs into the carotid sheath where it is joined by the sympathetic trunk to become the vagosympathetic trunk. The above pictures show this nerve where it has just split away from the sympathetic trunk as it enters the thoracic cavity. Spelling counts on this nerve, be sure to spell vagus correctly!

6 Larynx (specified structures) When we were in nursery school we called the larynx the voice box. It is made up of four major cartilages and houses the vocal cords. Functionally it is important because it connects the pharynx with the trachea, as well as being the structure where sound is produced. It extends between C4 and C6. Superiorly it is attached to the hyoid by the thyrohyoid ligament and inferiorly it is continuous with the trachea. Larynx Arytenoid Cartilage Dorsal view, right side The arytenoid cartilage is the only one of cartilages of the larynx that we will study that is split into two pieces. It forms the walls of the glottis and anchors the vocal cords. They cannot be seen from the outside of the larynx. Cricoid Cartilage Larynx Ventral view, right side The cricoid cartilage is also known as the signet ring cartilage. It is the only cartilage that forms a complete ring. It is narrow anteriorly and wide posteriorly. It is connected superiorly to the thyroid cartilage by the cricothyroid ligament and inferiorly to the trachea. It forms most of posterior wall of the larynx.

7 Epiglottic Cartilage Larynx Dorsal view The epiglottis or epiglottic cartilage is the superior most of the laryngeal cartilages. It projects superiorly and attaches to the tongue. Functionally it is important in humans because during swallowing it covers the opening of the larynx when the larynx moves superiorly. It has an obvious resemblance to Mick Jagger's tongue so many students refer to it as the Mick Jagger's tongue cartilage. Thyroid Cartilage Larynx Ventral view, right side When we were in nursery school we called the thyroid cartilage the Adam's apple. It is the largest of the laryngeal cartilages and larger in sexually mature males due to the effect of sex hormones. It is sometimes described as plow or shield shaped.

8 Parotid Salivary Gland and Duct Ventrolateral view, left side (gland) Ventrolateral view, left side (duct - quack) The parotid salivary gland is the largest of the salivary glands. It lies superficial to the masseter muscle and its duct passes across the masseter to deliver the saliva lateral to the second upper molar. As with most glands, it has a rough texture. Some students think it looks like the surface of cauliflower. It is an exocrine gland. Its secretions are controlled by the glossopharyngeal nerve (IX). Sublingual Salivery Gland Have you ever been gleeked? If so, you were the recipient of exocrine secretions from the sublingual salivary gland. In the cat it is situated deep to the mandibular (submaxillary) duct and the digastric muscle. It has its own ducts that open ventral to the tongue. It is the smallest of the salivary glands. In the human it is inferior to the tongue with 10 to 12 ducts opening into the oral cavity. Its secretions are controlled by the facial nerve (VII). It is about the size and shape of the tip of a Bic pen - in fact this may be where Bic pens come from!

9 Submaxillary (mandibular) Salivary Gland and Duct (gland) (duct - quack) The submaxillary (mandibular) salivary gland lies deep deep to the mandibular body anterior to the angle of the mandible in humans. Its duct opens lateral to the frenulum of the tongue. Its secretions are controlled by the facial nerve (VII). In the cat the duct runs on the deep medial side of the digastric muscle, superficial to the sublingual salivary gland. The gland looks like a gum drop without the sugar - or a dot (dart in some places in Rhode Island!) Thyroid Gland Ventral view, left side Lateral view, right side The thyroid gland is a bilobate endocrine gland. It is located inferior to the thyroid cartilage of the larynx and lateral to the trachea. It is the largest purely endocrine gland in the body. It produces two major hormones, thyroid hormone and calcitonin. They will be a topic for physiology. Notice: in the cat they look like rice peel offs. In fact, this may be where rice peel offs come from!

10 Trachea The trachea begins at the inferior end of the larynx (level of C6 body) and extends inferiorly to where it bifurcates into the left and right primary bronchi in humans. The inferior end is at the level of the sternal angle of humans in a supine position and to the body of T7 in the anatomical position. It is recognizable because of its 16 to 20 cartilaginous rings that normally prevent it from collapsing. The rings are not complete, being held together posteriorly by dense connective tissue. It is about 1.5" in diameter and is lined with ciliated epithelial cells that sweep mucous out of the trachea and into the pharynx. Ventral view Common Carotid Artery The common carotid arteries (left and right) are normally branches of the brachiocephalic artery, or less frequently branches of the bicarotid trunk. They are found in the carotid sheath on each side with the vagosympathetic trunk and the internal jugular vein. They have a number of branches, which will be discussed in turn. One of particular interest is the internal carotid artery. Although we will not observe this vessel because it is small in the cat, you should be aware of its significance. Eventually the common carotid artery bifurcates into the internal carotid and external carotid arteries and it is at t his point that there no longer is a common carotid artery. But the more important fact about the internal carotid artery is that it is one of two arteries from each side that serve the brain, the other being the vertebral artery that we discussed in the first lab and the third lab.

11 Cranial Laryngeal Artery The cranial laryngeal artery is a medial branch of the common carotid artery. It serves the cranial end of the larynx. It is just caudal to the tip of the pen in this picture. Cranial Thyroid Artery The cranial thyroid artery is the first medial branch of the common carotid artery that we will study. It serves the thyroid gland. I left the picture on the left in for orientation.

12 External Carotid Artery The external carotid artery and the internal carotid artery are the last two branches of the common carotid artery. It supplies blood to the structures of the head external to the cranial cavity. There are several branches of the external carotid artery that will be discussed in turn. The internal carotid artery will not be observed because in the cat it is very small, however, it is of significance for two reasons. First the common carotid artery bifurcates into the internal carotid and external carotid arteries and it is at this point that there no longer is a common carotid artery. But the more important fact about the internal carotid artery is that it is one of two arteries from each side that serve the brain, the other being the vertebral artery that we discussed in the first lab and the third lab. External Jugular Vein Lateral view, left side The external jugular vein in this lab is observed as it emerges from the deep side of the muscles in the neck and runs caudally until it meet the subclavian vein on the same side. This union forms the brachiocephalic vein on each side. Before that union occurs the internal jugular vein, which often does not take the dye, joins the external jugular vein. The external jugular vein receives blood from the head region except the cranial cavity.

13 External Maxillary Artery The external maxillary artery is a medial branch of the external carotid artery that arises cranial to the lingual (sublingual) artery. It runs deep to the digastric muscle and supplies blood to the salivary glands and the masseter muscle. Internal Jugular Vein Although the internal jugular vein is found in virtually all cats, it rarely takes the dye and it is relatively small. Because of this it is difficult to find. Typically, it is found in the carotid sheath, which also includes the common carotid artery and the vagosympathetic trunk. It usually joins the external jugular vein before the junction with the subclavian vein.

14 Lingual (sublingual) Artery The lingual (sublingual) artery is a medial branch of the external carotid artery. It runs with the hypoglossal nerve along the medial margin of the digastric muscle. Functionally it is important because it supplies the tongue with blood. Muscular Artery (branch) The muscular artery (branch) is a lateral branch of the common carotid artery. It leaves the common carotid close to the cranial thyroid artery and supplies blood to the muscles of the cervical region.