The Skeleton of the Anterior Limb. 



163 



radii) is immovably articulated with 

 the ulna. It bears an extensive 

 articular surface, meeting both the 

 trochlea and capitulum of the hum- 

 erus, and thus forming a considerable 

 portion of the elbow-joint. The body 

 of the bone is solidly united with the 

 ulna by the interosseous ligament 

 of the forearm. The distal extremity 

 is largely formed by an epiphysis, 

 which is well-marked even in older 

 animals. It bears a grooved, carpal 

 articular surface (fades articularis 

 carpea), for articulation with the 

 navicular and lunate bones. 



The ulna (Fig. 68) is a somewhat 

 S-shaped bone, the shaft of which is 

 vertically flattened, so that it pos- 

 sesses two main Slir faces, respectively 

 anterodorsal and posteroventral. The 

 former, in conjunction with the 

 related surface of the radius, continues 

 the area of origin of the extensor 

 muscles of the hand from the lateral 

 epicondyle of the htimerus distad on 

 to the forearm, while the latter has a 

 similar function with respect to the 

 flexor muscles. Theproximal portion 

 of the bone is laterally compressed. 

 It bears a crescentic depression, the 

 semilunar notch (incisura semi- 

 lunaris), the articulating surface of 

 which continues that of the medial 

 portion of the head of the radius, and 

 is received into the trochlea humeri. 

 Behind the elbow-joint the bone 

 forms ■ the large projecting portion 

 of the elbow, the olecranon, which is 

 a strong process for the insertion of 

 the extensor muscles (anconaei) 



Fig. 68. Skeleton of the fore- 

 arm and hand from the dorsal 

 surface: R, radius; U, ulna; C, 

 carpus; M, metacarpus; P, pha- 

 langes; I-V, metacarpal bones; c, 

 central' bone; cp., capitate; c.r., 

 head of radius; f.a.c, carpal artic- 

 ular surface of radius; h., hamate 

 bone; i.s., semilunar notch of the 

 ulna; 1., lunate bone; mi., lesser 

 multangular; mj., greater multang- 

 ular; n., navicular; ol., olecranon; 

 p^., styloid process of the ulna; 

 tr... triquetral bone; u., ungual 

 phalanges. 



