COMPARATIVE ANATOMY OF THE MUSCULAR SYSTEM 139 



each other. According to B there are five parts in the rabbit, and according to 

 R and J, four parts in the cat. Of these we may consider the following. 

 Rabbit: 



a) Pectoralis major. This is a large muscle originating from the whole length 

 of the sternum and inserted on the humerus. It covers most of the surface of 

 the chest, but the insertion is concealed by a muscle coming down from the head 

 (clavodeltoid) . Action, draws the arm toward the chest. 



b) Pectoralis primus. A slender muscle at the anterior end of the pre- 

 ceding and covering its anterior fibers. Origin, manubrium of the sternum; 

 insertion, humerus; action, like the preceding. Its anterior border is in contact 

 with the clavodeltoid, which also partly covers its insertion. 



c) Pectoralis minor. Cut through the middle of the belly of the pectoralis 

 major, and upon deflecting the cut edges note internal to it a similar muscle, 

 the pectoralis minor. Origin, manubrium; insertion, clavicle, and spine of the 

 scapula. To find the insertion loosen up the clavodeltoid and locate in its 

 fibers at the shoulder a small slender bone, the clavicle. The clavicle is on the 

 inner surface of the muscle. Then loosen the muscle next lateral to the clavodel- 

 toid, along muscle coming down from the back of the neck (anterior trapezius). 

 The pectoralis minor is inserted by some fibers on the clavicle, but most of its 

 fibers sweep over the shoulder internal to the clavodeltoid and anterior trapezius 

 and are inserted on the spine of the scapula. Action, draws arm and shoulder 

 toward the chest. 



Cat: 



a) Pectoantibrac/iialis. Anterior and most superficial of the chest muscles. 

 Origin, manubrium ; insertion, by a flat tendon on the fascia of the forearm; 

 action, draws the arm toward the chest. 



b) Pectoralis major. Next posterior to the preceding and extending ante- 

 riorly dorsal to the preceding which should be cut across; originating on the 

 sternum and median ventral raphe and inserted on the humerus. Action, like 

 the preceding. 



c) Pectoralis minor. Next posterior to the preceding and covered in large 

 part by the pectoralis major. The latter should be cut through and the extent 

 of the pectoralis minor noted. The pectoralis minor is divisible into several 

 parts. Origin, sternum; insertion, humerus; action, like the preceding. The 

 insertion cannot be fully traced at the present stage of the dissection. 



d) Xiphihumeralis. The last of the chest muscles, a thin flat long muscle, 

 passing from the xiphoid process of the sternum, its anterior part passing 

 dorsal to the posterior part of the pectoralis minor, and inserted on the humerus. 

 The insertion is covered by a mass of fat in the axilla. Remains of the cutaneous 

 maximus are probably present on its surface. Action, like the preceding. 



6. The muscles of the neck and throat. (Figs. 41 or 42.) Slit the skin up 

 the center of the throat to the tip of the lower jaw and loosen it so as to expose 



