FRONT OF THE FOREARM. 145 



descends along its outer side to the wrist : it here gives off 

 a branch which supplies the back of the hand, and then, 

 with the artery, passes over the annular ligament to the 

 palm of the hand. 



The flexor sublimis, flexor carpi ulnaris, and supinator longus mus- 

 cles, are now to be divided across their tendons, and their muscular 

 bellies reflected. The pronator radii teres may be drawn to one side 

 by hooks. The arteries and nerves should remain undivided. 



The FLEXOR PROFUNDUS DIGITORUM lies upon the ulna, 

 and arises from the upper two-thirds of that bone, and from 

 the interosseous membrane ; it divides into four tendons, 

 which are not, however, separable above the annular liga- 

 ment, beneath which they pass, and are inserted into the 

 bases of the last phalanges, having perforated the tendons 

 of the flexor sublimis. 



The FLEXOR LONGUS POLLICIS lies beneath the snpinator 

 longus muscle, and upon the radius; it arises from the 

 upper two-thirds of that bone, from the coronoid process 

 of the ulna, and ^from the interosseous membrane ; its 

 tendon passes beneath the annular ligament, and is in- 

 serted into the last phalanx of the thumb. 



The COMMON INTEROSSEOUS ARTERY, after arising from 

 the ulnar, quickly divides into two branches, anterior and 

 posterior. The anterior branch passes down the arm, be- 

 tween or in the deep flexor muscles, in close relation to the 

 interosseous membrane ; beneath the pronator quadratus 

 muscle the artery passes through this membrane to anasto- 

 mose with the posterior carpal branches of the ulnar and 

 radial. The posterior branch passes through the inter- 

 osseous membrane at its upper part, and is distributed to 

 the posterior aspect of the arm. 



The anterior interosseous nerve, a branch of the median, 

 accompanies the anterior interosseous artery, and termi- 

 nates in the pronator quadratus muscle. 



The PRONATOR QUADRATUS MUSCLE is a flat quadrilateral 

 muscle, stretched transversely across the lower part of the 

 bones of the forearm ; it arises from the anterior surface 

 and border of the ulna, and is inserted into the anterior sur- 

 face of the radius ; the insertion is usually a little narrower 

 than its origin. 



13 



