78 GENERAL ZOOLOGY 



The triceps brachii is an important muscle of the upper arm 

 whose contractions extend the forearm. A portion of it may be 

 seen in Fig. 47 at the posterior side of the upper arm. It arises 

 by three heads: (1) from the scapula and from the capsule of the 

 glenoid cavity; (2) from the proximal half of the inner surface of 

 the humerus; and (3) from the outer surface of the humerus. It 

 is inserted by a single tendon on the radioulna. The muscles 

 of the forearm consist of extensors and flexors of the wrist and 

 fingers, a description of which will be omitted. 



Muscles of the Head and Trunk, Dorsal Side. — A portion of 

 the temporalis muscle can be seen between the orbit and the 

 tympanum (Fig. 48). This muscle has its principal origin in 

 the prootic bone, from which it passes out beneath the squamosal 

 and over the pterygoid, between the latter and the maxillary 

 and quadratojugal to its insertion in the coronoid process of the 

 angulare. A portion of its fibers also come from the anterior 

 border of the tympanic ring and from the squamosal bone. It is 

 an important levator muscle of the lower jaw. The depressor 

 maxillae inferioris, overlapping the temporalis posteriorly, arises 

 (1) from the dorsal fascia and (2) from the squamosal and the 

 posterior and inferior border of the tympanic ring; it is inserted 

 in the posterior angle of the lower jaw. Its action depresses 

 the jaw and opens the mouth. The infraspinatus muscle, 

 arising from the suprascapula, and the latissimus dorsi, from 

 the dorsal fascia, are both inserted by a common tendon in the 

 outer surface of the deltoid ridge of the humerus. The longissi- 

 mus dorsi arises from the urostyle and is inserted in the spinous 

 processes of the first five vertebrae and in the lateral processes of 

 the first six vertebrae. The coccygeosacralis arises from the 

 anterior lateral surface of the urostyle and is inserted in 

 the neural arch and transverse process of the last vertebra. The 

 coccygeoiliacus arises from nearly the entire length of the urostyle, 

 and is inserted in the anterior two-thirds of the ilium. The 

 obliquus externus, a portion of which may be seen in the dorsal 

 view, has its origin in the scapula and the dorsal fascia, and its 

 insertion on the xiphisternum and in the rectus abdominis on the 

 ventral surface of the body. 



Muscles of the Thigh, Ventral Side. — The sartorius, a long 

 thin muscle traversing the mid ventral region of the thigh, arises 

 from the posterior end of the ilium and is inserted in the head 

 of the tibia, just beyond the knee joint. Its contraction pulls 



