THE SKELETON. 



55 



lar surface of the distal extremity consists of the capitellum, 

 for articulation with the head of the radius, and the trochleor 

 for articulation with the sigmoid cavity 

 of the ulna. On the cranial side of the 

 proximal third of the bone is the rough 

 deltoid ridge for the insertion of the 

 deltoid muscle which arises from the 

 shoulder girdle. 



The ulna is the longest bone of the 

 forearm or antebrachium, and is caudad 

 of the radius. It articulates in the greater 

 sigmoid cavity with the trochlea of the 

 humerus and in the lesser sigmoid cavity 

 with the head of the radius. The distal 

 articulation is with the radius, cuneiform 

 and pisiform (Fig. 21). The olecranon 

 process forms the proximal termination 

 of the bone and serves for the insertion 

 of the triceps muscle. Distad of the sig- 

 moid cavity is a projection known as the 

 coronoid process. The styloid process 

 forms a small projection on the distal 

 extremity of the bone. 



The radius is the preaxial or cranial 

 bone of the antebrachium. It articulates 

 proximally with the capitellum of the 

 humerus and the lesser sigmoid cavity 

 of the ulna, and distally with the scapho- 

 lunar and ulna. It bears but two proc- 

 esses, the tubercle and the styloid process. 

 The tubercle (Fig. 34) is a slight knot 

 near the proximal end on the ulnar side. 

 Proximal from the tubercle is the neck which supports the 

 head bearing a concave crown for articulation with the 



FIG. 33. LATERAL 

 OR OUTER AS- 

 PECT OF THE 

 RIGHT ULNA. 



ar, Articular facet 

 for radius ; cr, 

 coronoid proc- 

 ess ; gs, greater 

 sigmoid cavity ; 

 Is, lesser sigmoid 

 cavity; on, ole- 

 cranon process ; 

 st, styloid proc- 

 ess. 



