78 



RADIUS. 



Fig. 30.* 



visible into a shaft and two extremities : unlike the ulna, its upper 

 extremity is small, and merely accessory to the formation of the 

 elbow-joint; while the lower extremity is large, and 

 forms almost solely the joint of the wrist. 



The superior extremity presents a rounded head, 

 depressed upon its upper surface into a shallow cup. 

 Around the margin of 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 circumference, to play 

 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 at- 

 tachment of the tendon of the biceps; and smooth 

 above, where a bursa is interposed between the ten- 

 don and the bone. 



The shaft of the bone is prismoid, and presents 

 three surfaces. The anterior surface is somewhat 

 concave superiorly, where it lodges the flexor longus 

 pollicis ; and flat below, where it supports the pro- 

 nator quadratus. At about the upper third of this 

 surface is the nutritious foramen, which is directed 

 upwards. The posterior surface is round above, where 

 it supports the supinator brGvis muscle, and marked by several shal- 

 low 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 tube- 

 rosity 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 articular surfaces ; one at the side of the bone, which is con- 

 cave to receive the rounded head of the ulna ; the other at the ex- 

 tremity, and marked by a slight ridge into two facets, one exter- 

 nal and triangular, corresponding with the scaphoid; the other 

 square, with the semilunar bone. Upon the outer side of the ex- 

 tremity is a strong conical projection, the styloid process, which 

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

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

 its inner side to the triangular interarticular cartilage. 



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

 The greater sigmoid notch. 3. The lesser sigmoid not.ch, with which the head of the 

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

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

 membrane is attached. 8. The rounded head at the lower extremity of the ulna. 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. The lower extremity of the bone. 16. 

 Its styloid process. 



