3H VERTEBRATE ZOOLOGY 



minor. The former has its insertion in the hinder end of the skull ; 

 its posterior portion passes under the anterior trapezius to its 

 origin in the mid-dorsal ligament of the neck ; its action is to turn 

 and raise the head. The latter has its origin in the posterolateral 

 region of the skull, and its insertion in the posterodorsal angle of 

 the scapula ; its action is to rotate the shoulder. 



On the ventrolateral side of the neck will be seen the exposed 

 parts of several slender muscles, the action of which is to turn and 

 depress the head. They are the basioclavicularis muscle, imme- 

 diately ventral to the levator scapularis major, having its origin 

 in the basi-occipital bone of the skull, and its insertion in the 

 clavicle ; the cleidomastoid muscle, ventral to the basioclavicularis, 

 having its origin in the mastoid process of the skull, and its in- 

 sertion in the clavicle; the sternomastoid muscle, ventral to the 

 cleidomastoid, having its origin in the mastoid process of the skull, 

 and its insertion in the manubrium of the sternum. In the mid- 

 ventral region of the neck and ventral to the sternomastoids are 

 the two sternohyoid muscles, the origin of which is in the manu- 

 brium and the sternum, and the insertion in the hyoid bone. 



On the side of the head are two prominent muscles, the mas- 

 seter and the temporal, the function of which is to close the lower 

 jaw. The former lies beneath the eye and in front of the large 

 parotoid gland, and has its origin in the zygomatic arch of the skull 

 and its insertion in the mandible ; the latter lies in the temporal 

 fossa of the skull, above the ear, where it has its origin, the inser- 

 tion being in the hinder end of the mandible. 



On the shoulder and upper arm, portions of the deltoid and 

 triceps brachii muscles will be seen. The deltoid, of which there 

 are three parts, lies on the anterior side of the shoulder, one of 

 these parts appearing between the trapezius and the latissimus 

 dorsi, and another between the trapezius and the triceps; they 

 have their origin in the clavicle and the acromion and metacromion 

 processes of the scapula, and their insertion in the humerus. Its 

 action is to raise the arm. The triceps brachii— also in three parts, 

 which have their origin in the scapula and the humerus and their 

 insertion in the olecranon— lies on the back of the arm ; its action 

 is to extend the forearm. 



