108 



RADIUS. 



Fig 52.* 



upper surface into a shallow cup. Around the margin oi 

 the head is a smooth articular surface, which is broad on 

 the inner side, where it articulates with the lesser sigmoid 

 notch of the ulna, and narrow in the rest of its circumfer- 

 ence, to p ay in the orbicular ligament. Beneath the head 

 is a round constricted neck ; and beneath the neck, on its 

 internal aspect, a prominent process, the tuberosity. The 

 surface of the tuberosity is partly smooth, and partly rough ; 

 rough below, where it receives the attachment of the ten- 

 don of the biceps ; and smooth above, where a bursa is 

 interposed between the tendon and the bone. 



The shaft of the bone is prismoid, and presents three 

 surfaces. The anterior surface is somewhat concave su- 

 periorly, where it lodges the flexor longus pollicis ; and 

 flat below, where it supports the pronator quadratus. At 

 about the upper third of this surface is the nutritious fora- 

 men, which is directed upwards. The posterior surface 

 is round above, where it supports the supinator brevis 

 muscle, and marked by several shallow oblique grooves 

 below, which afford attachment to the extensor muscles 

 of the thumb. The external surface is rounded and con- 

 vex, and marked by an oblique ridge, which extends from 

 the tuberosity to the styloid process at the lower extremity 

 of the bone. Upon the inner margin of the bone is a sharp and prominent 

 crest, which gives attachment to the interosseous membrane. The lower 

 extremity of the radius is broad and triangular, and provided with two ar- 

 ticular surfaces ; one at the side of the bone, which is concave to receive 

 the rounded head of the ulna ; the other at the extremity, and marked by 

 a slight ridge into two facets, one external and triangular, corresponding 

 with the scaphoid ; the other square, with the semilunar bone. Upon the 

 outer side of the extremity is a strong conical projection, the styloid process, 

 which gives attachment by its base to the tendon of the supinator longus, 

 and by its apex to the external lateral ligament of the wrist joint. The 

 inner edge of the articular surface affords attachment to the base of the 

 inter-articular cartilage of the ulna. 



Immediately in front of the styloid process is a groove, which lodges 

 the tendons of the extensor ossis metacarpi pollicis, and extensor primi 

 internodii ; and behind the process a broader groove, for the tendons of 

 the extensor carpi radialis longior and brevior, and extensor secundi inter- 

 nodii ; behind this is a prominent ridge, and a deep and narrow groove, 

 for the tendon of the extensor indicis ; and still farther back, part of a 

 broad groove, completed by the ulna, for the tendons of the extensoi 

 communis digitorum. 



Development. By three centres ; one for the shaft, and one for each ex- 

 tremity. Ossification commences in the shaft soon after the humerus, and 

 before that in the ulna. The inferior centre appears during the second 



* The two bones of the fore-arm seen from the front. 1. The shaft of the ulna. 2. 

 The greater sigmoid notch.; v 3. The lesser sigmoid notch, with which the head of the 

 radius is articulated. 4. The olecranon process. 5. The coronoid process. 6. The nu- 

 tritious foramen. 7. The sharp ridges upon the two bones to which the interosseous 

 membrane is attached. 8. The rapitulum ulnae. 9. The styloid process. 10. The 

 shaft of the radius. 11. Its head surrounded by the smooth border for articulation with 

 the orbicular ligament. 12. The neck of the radius. 13. Its tuberosity. 14. The oblique 

 line 15. Tire lower extremity of the bone 16. Its styloid process. 



