144 THE SUPERIOR EXTREMITY 



the proximal border of the interosseous membrane to the 

 dorsal part of the forearm, where it will be dissected at a 

 later period. 



The arteria interossea volaris descends on the anterior 

 surface of the interosseous membrane, between the adjacent 

 margins of the flexor pollicis longus and the flexor digitorum 

 profundus, which must be separated as the artery is followed. 

 At the proximal border of the pronator quadratus it pierces 

 the interosseous membrane and passes to the dorsal part 

 of the forearm, where its terminal part will be seen at a 

 later period. As it descends on the volar surface of the 

 interosseous membrane it gives twigs to the adjacent muscles, 

 and the following named branches : 



i. Arteria mediana. 



2 and 3. Nutrient to radius and ulna. 



4. Volar communicating. 



The arteria mediana is a long slender vessel which 

 accompanies the median nerve to the palm of the hand, 

 where it sometimes terminates in the superficial volar arch. 

 The nutrient arteries enter the nutrient foramina of the 

 radius and ulna. The volar communicating artery descends 

 on the volar surface of the interosseous membrane, deep to 

 the pronator quadratus, to the carpus, where it terminates in 

 the volar carpal arch. 



The ulnar carpal arteries are two small arteries, which 

 partially encircle the wrist. The volar ulnar carpal artery 

 runs laterally, under cover of the tendons of the flexor digi- 

 torum profundus, and anastomoses with the volar carpal 

 branch of the radial artery. From the arch, thus formed, 

 small twigs are given to the volar aspect of the carpal bones 

 and joints. The dorsal ulnar carpal artery gains the dorsal 

 aspect of the carpus by winding round the medial margin of 

 the limb immediately proximal to the pisiform bone, and 

 under cover of the tendon of the flexor carpi ulnaris. 



Nervus Ulnaris. The ulnar nerve, which was traced in 

 the dissection of the arm as far as the interval between the 

 olecranon and medial epicondyle of the humerus, enters the 

 forearm between the two heads of the flexor carpi ulnaris. It 

 proceeds distaliy, on the volar surface of the flexor digitorum 

 profundus and under cover of the flexor carpi ulnaris, in the 

 volar part of the medial side of the forearm. Close to 



