RADIUS. 



695 



The upper extremity, styled the head, presents two 

 smooth articulating surfaces; the one, a superficial cavity, 

 and superior, articulates with the small head FIG. 218. 

 of the huinerus; the other forms the circum- 

 ference and articulates with the lesser sig- 

 moid cavity of the ulna. Below the head the 

 bone contracts, and is called the cervix or 

 neck. Below the neck, or where the latter 

 and the body unite, is the tubercle which 

 gives insertion to the tendon of the biceps. 

 It is also covered by a bursa. The lower or 

 carpal extremity is the larger of the two, 

 and is widest transversely. It is bounded 

 externally by the styloid process, which gives 

 attachment to the external lateral ligament 

 of the wrist. Internally is a smooth concave 

 surface for articulating with the lower end 

 of the ulna. The carpal surface is smooth 

 and divided by a ridge into two unequal articulating 

 portions ; the outer and larger is for the scaphoid bone, 

 the inner receives the lunar. The margin of the carpal 

 surface presents a prominent ridge to which the capsular 

 ligament is attached. On the posterior surface of this car- 

 pal extremity several grooves are noticed. At the side and 

 base of the styloid process is a groove for the tendons of the 

 extensor ossis metacarpi, and minor pollicis muscles. Next 

 to this is a larger groove for the tendons of the exten- 

 sor carpi radialis longior and brevior. On the middle, and 

 next in order, is a groove for the extensor major pollicis, 

 and on the ulnar side of this is another and larger for the 

 extensor communis and indicator. Structure. Cellular in 

 the extremities and compact in the centre. 



FIG. 218 represents the Radius'and Ulna, a Shaft of the ulna. 6 The greater 

 sigmoid cavity, c Lesser sigmoid cavity. dOlecranon process- Coronoii 

 process. /Nutritious foramen, g Sharp edge for attachment of interosseous 

 membrane, h Lower extremity of ulna, t Styloid process, j Shaft of radius, 

 fc Its head. /Neck, m Its tuberosity. n Oblique line, o Lower extremity of 

 radius, pits styloid process. 



