246 THE ARM AND FORE-ARM. [chap. 



though not usually, perforated. The lower articular surface 

 is divided by a groove into a pulley-like internal portion 

 {trochlea) for the ulna, and a smallel" rounded portion {capi- 

 tcliinn), confined to the front side of the bone, for the radius. 



The whole bone is somewhat twisted on its longitudinal 

 axis. Supposing it is so placed that a line drawn hori- 

 zontally through the axis of the head passes directly back- 

 wards, another line drawn through the condyles would 

 not cross this at a right angle, as in most of the inferior 

 Mammals, but its outer end would be directed forwards. 



The radius has the head or proximal end expanded, disk- 

 shaped, and cupped at its extremity, which is applied to 

 tlie capitellum of the humerus (see Fig. 82). Below this 

 expanded head the bone is comparatively slender, but 

 increases in size as it approaches the lower end, which is 

 wide from side to side ; the surface next the ulna being 

 hollowed to receive the lower end of that bone, while the 

 opposite side is produced into the radial styloid process. 

 The inferior surface is hollowed for articulation with the 

 carpus. The whole bone is slightly curved. Not far below 

 the head is a rough prominence, into which the tendon of 

 the biceps flexor muscle is inserted. 



The ulna has a large sigmoid excavation above for 

 articulation with the trochlea of the humerus ; the pointed 

 elevated anterior edge of this is called the coi'onoid ptvcess. 

 The olecranon is scarcely i)roduced upwards beyond the 

 hinder edge of the articular surface. Below this, on the radial 

 side, is a smaller excavation, in which the edge of the disk- 

 hke head of the radius plays, being held in its place in the 

 living state by a strong annular ligament, which encircles 

 it. The ulna is straighter than the radius, and gradually 

 diminishes in size to the lower end, where it terminates in a 

 rounded surface, which articulates with the hollow in the 



