THE SKELETON 



6S 



only orders in which all the species possess clavicles. A third 

 element of the shoulder girdle, known as the coracoid, is a fully 

 developed bone only in the Mono- 

 tremata, where it articulates at one 

 end with the scapula, forming part of 

 the glenoid cavity, and at the other 

 end with the presternum. In the 

 other mammals the coracoid is rep- 

 resented by the coracoid process of 

 the scapula, which ossifies from a 

 separate center. In many of the 

 lower vertebrates a distinct coracoid is 

 present. 



The humerus is the bone of the arm 

 or brachium. It articulates proximally 

 with the glenoid cavity of the scapula 

 (Fig. 22) and distally with the ulna and 

 radius. It consists of three parts, the 

 proximal extremity bearing the head, 

 the middle portion or shaft, and the 



. /-r^. X rr^i Fig. 33.— Cranial Aspect 



distal extremity (Fig. 33). The greater of Right Humerus. 

 and lesser tuberosities separated by the ^^' ^'Tl^^^l ^':°°^^"' 'I' 



^ -^ supracondyloid ridge; cp, 



bicipital groove lodging the tendon ofcapitulum for articulation 

 . 1 , . , .1 . with the radius: dr, deltoid 



the biceps muscle, are the two processes ^-idge; et, external condyle; 



on the proximal extremity. The for-s^- greater tuberosity; it. 



internal condyle; It, lesser 



mer is the larger and more craniad tuberosity; sp, supracondy- 

 and serves tor the insertion of the'^,J:^'Z:mZ .r'sut 



SUpraSpinatUS muscle (Fig. 55). The inator ridge; /r, trochlea for 

 ... . . Ill • articulation with ulna. 



distal extremity is marked by two im- 

 portant projections, the external and internal condyles. Ex- 

 tending proximad from the external condyle is the supinator 

 ridge. Proximad of the internal condyle is the supracondyloid 

 foramen transmitting the median nerve and branchial artery 

 (Figs. 78 and 100). The olecranon fossa is the deep cavity on the 

 caudal aspect of the bone, opposite the coronoid fossa. The 



