ANTERIOR BRACHIAL REGION. 



309 



The Flexor Longus Polli- 

 cis is situated on the radial 

 side of the forearm, lying on 

 the same plane as the preced- 

 ing. It arises from, the up- 

 per two-thirds of the grooved 

 anterior surface of the shaft 

 of the radius; commencing, 

 above, immediately below the 

 tuberosity and oblique line, 

 and extending, below, to with- 

 in a short distance of the 

 Pronator quadratus. It also 

 arises from, the adjacent part 

 of the interosseous membrane, 

 and occasionally by a fleshy 

 slip from the inner side of the 

 base of the coronoid process. 

 The fibres pass downwards 

 and terminate in a flattened 

 tendon, which passes beneath 

 the annular ligament, is then 

 lodged in the interspace be- 

 tween the two heads of the 

 Flexor brevis pollicis, and 

 entering a tendino-osseous ca- 

 nal, similar to those for the 

 other flexor tendons, is in- 

 serted into the base of the last 

 phalanx of the thumb. 



Relations. By its anterior 

 surface, with the Flexor sub- 

 limis digitorum, Flexor carpi 

 radialis, Supinator longus, and 

 radial vessels. By its poste- 

 rior surface, with the radius, 

 interosseous membrane, and 

 Pronator quadratus. By its 

 ulnar border, with the Flexor 

 profundus digitorum, from 

 which it is separated by the 

 anterior interosseous vessels 

 and nerve. 



The Pronator Quadratus 

 is a small, flat muscle, quadri- 

 lateral in form, extending 

 transversely across the front 

 of the radius and ulna, above 

 their carpal extremities. It 

 arises from the oblique line 

 on the lower fourth of the 

 anterior surface of the shaft 

 of the ulna, and the surface of 

 bone immediately below it; 

 from the internal body of the 

 ulna; and from a strong apo- 

 neurosis which covers the 



Fig. 173. Front of the Left Forearm. Deep Muscles. 



