FOREARM AND HAND 109 



medial aspects of the ulna; the flexor pollicis longus is placed 

 upon the volar surface of the radius; while the pronator 

 quadratus is a quadrate fleshy layer closely applied to both 

 bones immediately proximal to the wrist. The artery and 

 nerve proceed distally in the interval between the flexor pro- 

 fundus and flexor pollicis longus. 



M. Flexor Digitonun Profundus. The deep flexor of 

 the fingers springs from the volar and medial surfaces of 

 the ulna in its proximal three -fourths. It likewise derives 

 fibres from the volar surface of the interosseous membrane 

 and the aponeurosis by which the flexor carpi ulnaris takes 

 origin from the dorsal border of the ulna. The fleshy mass 

 gives place to four tendons for the four medial digits, but 

 only one of these that for the index finger becomes 

 separate and distinct in the forearm. They proceed distally, 

 deep to the transverse carpal ligament, into the palm. The 

 flexor digitorum profundus is supplied by the volar interosseous 

 branch of the median and by the ulnar nerve. 



M. Flexor Pollicis Longus. The flexor pollicis longus 

 arises from the volar surface of the radius, over an area 

 which extends from the volar border above to the proximal 

 border of the pronator quadratus below. It also takes origin 

 from the adjacent part of the volar surface of the interosseous 

 membrane. A rounded tendon issues from the fleshy belly, 

 and proceeds into the palm, under cover of the transverse 

 carpal ligament. 



In many cases the flexor pollicis longus will be observed 

 to have an additional slender head of origin, from the medial 

 border of the coronoid process of the ulna, or the medial 

 epicondyle of the humerus. The flexor pollicis longus is 

 supplied by the volar interosseous nerve. 



M. Pronator Quadratus. This is a quadrate muscle which 

 takes origin from the volar surface of the ulna in its distal 

 fourth, and is inserted into the volar aspect of the distal 

 end of the radius. It is supplied by the volar interosseous 

 nerve. 



Arteria Interossea Volaris (O.T. Anterior Interosseous 

 Artery). The volar interosseous artery has been seen to 

 arise from the common interosseous artery. It runs distally 

 upon the volar surface of the interosseous membrane, in the 

 interval between the flexor pollicis longus and the flexor 

 digitorum profundus. At the proximal border of the pronator 



