140 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



fully the lower jaw. Note in doing so parts of the platysma muscle on the under 

 side of the skin. It sweeps from the median dorsal line of the neck around the 

 sides of the head to face and ears, and portions of it generally are attached near 

 the anterior end of the sternum. In dissecting the throat muscles work on 

 one side only, leaving the other intact for the study of other parts. Avoid 

 cutting any blood vessels. A large vein, the external jugular vein, runs in 

 the superficial muscles of the throat. At the angle of the jaw is a rounded 

 pinkish body, the submaxillary gland, one of the salivary glands. Other small 

 bodies are lymph glands. 

 Rabbit: 



a) Special portion of the platysma. A broad thin sheet of dermal muscle 

 extends from the manubrium of the sternum forward, forking like the letter V, 

 each half inserting at the base of the ear. This is the depressor conchae posterior 

 and is the most superficial muscle on the ventral surface of the neck. The 

 external jugular vein runs in it. It is a part of the platysma. It should be 

 well separated from the underlying muscles and the posterior end severed and 

 turned forward, without, however, injuring the vein. 



b} Sternohyoid. This is the long muscle in the median line of the neck, 

 the two members of the pair being closely fused in the median ventral line. 

 Origin, manubrium of the sternum; insertion, anterior horn of the hyoid. Follow 

 the muscle up to the throat and feel with the fingers the bony hyoid on which 

 the muscle is inserted. Action, draws the hyoid posteriorly or raises the sternum. 



c] Sternomastoid. The long muscle on each side of the preceding, the two 

 members of the pair converging toward the manubrium of the sternum from 

 which they originate ventral to the origin of the preceding. Insertion, mastoid 

 process of the skull; action, singly turn the head, together depress the head on 

 the neck. 



d) Cleidomastoid and basioclavicularis. These two long strap-shaped muscles 

 are next lateral to the preceding and unite at the clavicle with the clavodeltoid. 

 The cleidomastoid is the more medial one and lies lateral and somewhat dorsal 

 to the Sternomastoid. Origin, mastoid region of the skull; insertion, clavicle; 

 action, elevates clavicle or turns the head. The basioclavicularis is slightly 

 lateral to the preceding at its cranial end but crosses ventral to it caudally so 

 that its insertion on the clavicle is medial to that of the cleidomastoid. Origin, 

 occipital bone; insertion, clavicle; function, like preceding. The origins of these 

 muscles cannot be followed out conveniently. 



e} Clavodeltoid. Continuation of the two preceding muscles. Origin, 

 clavicle; insertion, humerus; action, raises the humerus. 



/) Masseter. The great mass of muscle covering the angle of the jaws, its 

 outer surface with a very tough shining fascia. Origin, zygomatic arch ; inser- 

 tion, outer surface of the posterior end of the mandible; action, closes the lower 

 iaw (elevator of the jaw.) 



