192 VERTEBRATE ZOOLOGY 



ment to the breastbone and the coracoid, which is the larger bone 

 joining the breastbone with the shoulder blade, and follow the 

 tendon to its insertion in the dorsal side of the humerus. Be care- 

 ful not to injure any of these bones while dissecting the muscles. 



Test the action of both pectoral muscles; the great pectoral 

 will be seen to depress the wing, and the lesser pectoral to raise it. 



The abdominal muscles are of much smaller extent in birds than 

 in mammals, on account of the large size of the breast muscles. 

 They consist of the right and left external obliques, which form 

 the outer surface of the abdomen and whose fibers run diagonally ; 

 the internal obliques, which lie beneath the external obliques and 

 whose fibers run at right angles to their fibers; the transverse 

 muscles, which are the innermost and whose fibers run trans- 

 versely; and the rectus abdominis muscles, which occupy the 

 median area. All these muscles are more or less rudimentary 

 and tendinous, their fibers having disappeared and the mem- 

 branous fasciae and tendons alone being present in portions of 

 them. The rectus abdominis has entirely lost the metamerism 

 which characterizes it in amphibians and mammals. These mus- 

 cles will not be dissected. Observe as many of these features 

 as possible. 



On the ventral side of the head note the submandibular muscle, 

 the fibers of which run transversely across the throat ; its median 

 portion is tendinous. 



In the proximal division of the wing (the upper arm) are the 

 large biceps muscle on the anterior side and the large triceps on the 

 posterior side ; these muscles act as the chief flexor and extensor 

 respectively of the forearm. 



In the middle division (the forearm) the following muscles ap- 

 pear on the ventral surface, beginning with the anterior border : the 

 extensor radialis, the pronator brevis, the pronator longus (the dis- 

 tal end only of which appears), the short cubitocarpalis profundus, 

 the long extensor carpi ulnaris, and the large flexor carpi ulnaris, 

 which forms the posterior border. Determine, by following the 

 tendons, which of these muscles extend and which flex the hand. 



In the ventral surface of the proximal division of the leg (the 

 thigh), beginning at the anterior border, are the following muscles : 



