THE SKELETON. 



6 9 



malia. The clavicle is never fully developed in any of 

 the Carnivora . Primates , Chir op ter a , 

 Edentata, and Monotremata are the 

 only orders in which all the species 

 possess clavicles. A third element of 

 the shoulder girdle, known as the cora- 

 coid, is a fully developed bone only in 

 the Monotremata, 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 

 represented by the coracoid process 

 of the scapula, which ossifies from a 

 separate center. In many of the lower 

 vertebrates a distinct coracoid is pres- 

 ent. 



The humerus is the bone of the arm 

 or brachium. It articulates proxi- 

 mally with the glenoid cavity of the 

 scapula (Fig. 2 1 ) 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 distal extremity (Fig. 32). The 

 greater and lesser tuberosities separated 

 by the bicipital groove lodging the 

 tendon of the biceps muscle, are the 

 two processes on the proximal ex- 

 tremity. The former is the larger 

 and more cephalic, and serves for the 

 insertion of the supraspinatus muscle 

 (Fig. 49). The distal extremity is marked by two im- 

 portant projections, the external and internal condyles. 



FIG. 32. --CEPHALIC 

 ASPECT OF RIGHT 

 HUMERUS. 



bl, Bicipital groove ; cr, 

 supracondyloid 

 ridge ; cp, capitellum 

 for articulation with 

 the radius; dr, del- 

 toid ridge; et, ex- 

 ternal condyle ; gt, 

 greater tuberosity ; 

 it, internal condyle; 

 It, lesser tuberosity; 

 sp, supracondyloid 

 foramen or entepi- 

 condylar foramen ; 

 sr, supinator ridge; 

 tr, trochlea for ar- 

 ticulation with ulna. 



