ANTERIOR BRACHIAL REGION. 



387 



The Flexor Longus Pollitis is 

 situated on the radial side of the 

 forearm, lying on the same plane as 

 the preceding. It arises from the 

 upper two-thirds of the grooved 

 anterior surface of the shaft of the 

 radius; commencing, above, im- 

 mediately below the tuberosity 

 and oblique line, and extending, 

 below, to within 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 termi- 

 nate in a flattened tendon, which 

 passes beneath the annular liga- 

 ment, is then lodged in the inter- 

 space between the two heads of 

 the Flexor Brevis Pollicis, and 

 entering a tendino-osseous canal 

 similar to those for the other 

 flexor tendons, is inserted into 

 the base of the last phalanx of 

 the thumb. 



Relations. By its anterior sur- 

 face, with the Flexor Sublimis 

 Digitorum, Flexor Carpi Radialis, 

 Supinator Longus, and radial ves- 

 sels. By its posterior surface, with 

 the radius, interosseous mem- 

 brane, 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, quadrilateral muscle, 

 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 border 

 of the ulna; and from a strong 

 aponeurosis which covers the in- 

 ner third of the muscle. The 

 fibres pass horizontally outwards, 

 to be inserted into the lower 

 fourth of the anterior surface and 

 external border of the shaft of 

 the radius. 



Fig. 240. Front of Left Forearm. Deep Muscles. 



