RADIUS. 



81 



parated from the cuneiform bone of the carpus by the triangular inter- 

 articular cartilage. 



Attachment of Muscles. To twelve ; by the olecranon, to the triceps 

 extensor cubiti, one head of the flexor carpi ulnaris, and the an- 

 coneus ; by the coronoid process, to the brachialis anticus, pronator 

 radii teres, flexor sublimis digitorum, and 

 flexor profundus digitorum ; by the shaft, to Fig. 36.* 



the flexor profundus digitorum, flexor carpi 

 ulnaris, pronator quadratus, anconeus, extensor 

 carpi ulnaris, extensor ossis metacarpi pollicis, 

 extensor secundi internodii pollicis, and ex- 

 tensor indicis. 



RADIUS. The radius is the rotatory bone 

 of the fore-arm ; it is divisible 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 attachment of the tendon 

 of the biceps ; and smooth above, where abursa 

 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 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 nu- 

 tritious foramen, which is directed upwards. Ths posterior surface is 



* 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 notch, 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 capitulum 

 ulnae. 9. The styloid process. 10. The shaft of the radius. 11. Its head sur- 

 rounded 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. 



G 



