Limbs : Upper Limb 



99 



muscle may be prolonged down to the outer border to within 2 or 3 inches of the lower 

 end of the bone, and may be muscular here. 



The oblique line behind may be also considered a primary structure with a secon- 

 dary line on it that is often not appreciab'e. 



The Supinator brevis is inserted as shown in the figures, but makes no marking on 

 the bone save near the lower part 

 of its area, for this is as a ru'e the 

 only part where tendinous fibres 

 are to be found in it. It extends 

 down to the top of the impression 

 for Pronator teres, which is more 

 on the back than the front of the 

 outer side of the bone. 



The flexor surface has a very 

 faint quadrate ridge, due only to 

 attachment of aponeurotic fasciae 

 of the muscle, and not, as in the 

 ulna, to implantation of fibres of 

 the interosseous membrane. 



The Pronator quadratus has 

 a large area of insertion, reaching 

 out to the outer margin and down 

 to the rough ligamentous ridge : 

 internally it extends to the inner 

 margin and round this on to the 

 triangular area that lies above the 

 sigmoid notch. 



The extensor area gives origin 

 to two of the deep muscles, and 

 a faint indication of the position 

 of the muscles running downwards 

 and outwards may be found by 

 the finger and sometimes by the 

 eye. Below the surface for origin 

 of Ext. brevis pollicis is an area 

 covered by Ext. longus pollicis and 

 Ext. indicis, but not giving origin to 

 them : deep to these the anterior 

 interosseous artery and posterior 

 interosseous nerve lie on the 

 bone. 



The outer aspect of the 

 radius is covered by Supinator 



brevis in its upper half, then by the tendon of Pronator teres, and below this by 

 the radial extensor and Supinator longus tendons which have passed down over the 

 Supinator brevis and Pronator tendon. These are shown in Fig. 79. At the lower 

 end of the radius the mass that ends in the styloid process projects outwards, nearer 

 the front than the back of the bone, so that the outer surface now becomes postero- 

 external, while a new outer surface is made on the prominent mass. Thus the Radial 

 Extensor tendons come to lie in the postero-external groove on the lower end, while 



FIG. So. The upper right figure is of the head of the ulna 

 seen from below. The others are of the lower end of 

 the radius from behind, from the inner side, and from 

 the outer side, i, groove for Ext. comm. dig., Ext. 

 indicis, ant. inteross. artery and post inteross. nerve ; 

 2, for Ext. sec. internod. (longus poll.) ; 3, for radial 

 extensors ; 4, for Ext. oss. metacarpi (a) and Ext. 

 primi internod. (breviS pollicis) (6). x marks attach- 

 ment of posterior annular ligament. On the inner 

 side the dotted line shows the extent of the synovial 

 cavity ; this goes up to the insertion of Pronator 

 quadratus above but does not reach the margin below 

 because the triangular cartilage is attached here. On 

 the outer side notice the insertion of Supinator longus 

 partly covered by tendon of Ext. ossis metacarpi 

 pollicis. 



