THE EADIUS. 



215 



TRICEPS 



which rolls within the radial notch of the ulna in the movements of pronation 

 and supination. The character of the lateral half of the circumference differs from 

 the medial, in being narrower, and rounded proxinio-distally. 



The collum radii (neck) is the constricted part of the body which supports the 

 head, the overhang of the latter being greatest towards the lateral and dorsal side. 

 Distal to the neck, on the medial side, there is an outstanding oval -prominence, 

 the tuberositas radii (radial tuberosity). The dorsal part of this is rough for 



the insertion of the biceps tendon, whilst the volar 

 half is smooth and covered by a bursa which inter- 

 venes between it and the tendon. 



The body (corpus radii), which has a lateral 

 curve and is narrow proximally and broad distally, 

 is wedge-shaped on section. The edge of the wedge 

 forms the sharp medial interosseous crest of the bone 

 (crista interossea), whilst its base corresponds to the 

 thick and rounded lateral border over which the 

 volar or anterior surface becomes confluent with the 

 dorsal or posterior surface. 



The interosseous crest, faint proximally where it 

 lies in line with the dorsal margin of the tuber- 

 osity, becomes sharp and prominent in the middle 

 third of the bone. Distal to this it splits into two 

 faint lines, which lead to either side of the ulnar 

 g notch on the distal end of the bone, thus includ- 

 ing between them a narrow triangular area into which 

 the deeper fibres of the pronator quadra tus muscle 

 are inserted. To this crest, as well as to the 

 * dorsal of the two divergent lines, the interosseous 

 membrane is attached. 



The lateral surface (once described as the 

 lateral border) is thick and rounded proximally, 

 but becomes thinner and more prominent distally, 

 where it merges with the base of the styloid 

 process. About its middle the anterior and posterior 

 oblique lines become confluent with it, and here, 

 placed between them, is a rough elongated impres- 

 sion which marks the insertion of the pronator teres 

 muscle. Proximal to this, and on the 

 RADIAL EXTENSORS lateral surface of the neck, the 

 supinator muscle is inserted, whilst 

 distally this surface is overlain by 

 the tendons of the brachio-radialis 

 and the extensor carpi radialis longus 

 and brevis muscles. 



The volar or anterior surface 

 (facies volaris) is crossed obliquely 

 by a line which runs from the 



f,,^,^;^ rHstallv and latprallv 

 tuberosity CfcStoJly ana later 



towards the middle of the lateral 

 i surface of the body. This, often called the anterior oblique line, serves for the attach- 

 I ment of the radial head of origin of the flexor digitorum sublimis muscle. Proximal 

 to it, the volar aspect of the bone has the fibres of the supinator muscle inserted 

 into it, whilst distal and medial to it, extending as far as the distal limit 

 i of the middle third of the bone, is an extensive surface for the origin of the 

 i flexor pollicis longus muscle. In the distal fourth of the bone, where the volar 

 aspect of the body is broad and flat, there is a surface for the insertion of the 

 pronator quadratus muscle, which also extends dorsally to the interosseous ridge. 



The dorsal or posterior surface (facies dorsalis) is also crossed by an 

 oblique line,, less distinct than the anterior. This serves to define the proximal 



ABDUCTOR POLLICIS 

 LONGUS AND EXTENSOR 



POLLICIS BREVIS 



EXTENSOR DIGITORUM COMMUNSI 

 AND EXTENSOR INDICIS PROPRIUS 



EXTENSOR POLLICIS LONGUS 



, FIG. 207. DORSAL ASPECT OF BONES OF RIGHT FORE- 

 ARM WITH ATTACHMENTS OF MUSCLES MAPPED OUT. 



