THE FOREARM AND WRIST 73 



with the exception of the flexor carpi ulnaris, and by means of 

 its volar interosseous branch it supplies the deep muscles of the 

 front of the forearm. Injuries of the nerve are discussed on 

 p. 104. 



The Deep Group of Muscles (Flexor pollicis longus, Flexor digitorum 

 profundus, and Pronator quadratus) is supplied by the volar interosseous branch 

 of the median nerve (C. 7, 8,. and T. i), with the exception of that portion 

 of the flexor digitorum profundus destined for the ring and little fingers, 

 which is supplied by the ulnar nerve (C. 8 and T. i). 



The Extensor and Supinator Muscles. The Brachio - radialis, 

 which is inserted into the distal part of the lateral surface of the radius, and 

 the Extensor carpi radialis longus are both supplied by the radial (musculo- 

 spiral) nerve (C. 5 and 6, C. 6 and 7, respectively). The former is a flexor 

 of the forearm ; in the movement of supination it assists until the mid-prone 

 position is reached, and it also assists pronation from the supine to the mid- 

 prone position. 



The Supinator (S. brevis) winds round the posterior aspect of the proximal 

 part of the radius and is thus a powerful supinator. It is supplied by the 

 deep branch (posterior interosseous) of the radial (musculo-spiral) nerve (C. 6). 



The Ancon&us covers the posterior aspect of the humero-radial joint, 

 and is supplied by a branch from the radial (musculo-spiral) nerve (C. 7 and 8). 



The Superficial Group of Extensors arises from the distal part of the 

 anterior aspect of the lateral epicondyle of the humerus, and they are supplied 

 by the dorsal interosseous nerve (C. 6, 7, and 8). 



This group comprises the Extensor carpi radialis brevis (p. 68), the Extensor 

 digitorum communis (p. 92), the Extensor digiti quinti proprius (p. 92), and 

 the Extensor carpi ulnaris (pp. 69, 81). 



The Deep Group of Extensors arises from the dorsal surfaces of the 

 radius and ulna. They are all supplied by the dorsal interosseous nerve 

 (C. 6, 7, and 8). 



The Abductor Pollicis Longus (extensor ossis metacarpi pollicis) (pp. 67, 75) 

 is inserted into the base of the metacarpal bone of the thumb. It extends 

 the thumb at the carpo-metacarpal joint. 



The Extensor Pollicis Brevis and Longus (pp. 68, 75) are inserted into 

 the bases -of the first and second phalanges respectively. Primarily they 

 are extensors, but they also aid in abduction of the thumb. 



The Extensor Indicis Proprius (p. 92). 



The Dorsal Interosseous Nerve reaches the back of the 

 forearm by winding round the neck of the radius, in the substance 

 of the supinator (s. brevis), its course being at right angles to 

 the direction of the muscle fibres. On leaving the muscle 

 (p. 67) the nerve breaks up into branches which are distributed 

 to the remaining muscles on the back of the forearm. 



Surgical Approach to the Bones of the Forearm. 

 The Ulna may be exposed readily in any part of its extent by 

 incisions along its subcutaneous dorsal border. 



The Radius may be exposed by incisions along the line 

 which separates the radial extensors of the wrist from the 

 extensor digitorum communis (p. 67). 



