142 THE SUPERIOR EXTREMITY 



Dissection. Cut through the radial part of the flexor digi- 

 torum sublimis at its union with the humeral portion. Pull 

 the main mass of the muscle towards the medial side of the 

 forearm, and turn the radial portion towards its origin. Then 

 clean the median nerve, the branch of the anterior interosseous 

 artery which accompanies the nerve, and the anterior surface 

 of the flexor pollicis longus which springs from the volar surface 

 of the radius ; and the flexor digitorum profundus, which arises 

 from the volar and medial surfaces of the ulna. Then secure the 

 volar interosseous branch of the median nerve. It springs from 

 the median nerve as the latter emerges from between the two 

 heads of the pronator teres. Find also the common interosseous 

 branch of the ulnar artery. It arises in, or immediately distal 

 to, the cubital fossa, and must be looked for behind the deep head 

 of the pronator teres. Almost at once it divides into volar and 

 dorsal interosseous branches. The dorsal branch passes backwards 

 above the interosseous membrane to the dorsal part of the fore- 

 arm, where it will be dissected later. Now separate the adjacent 

 borders of the flexor pollicis longus and the flexor digitorum 

 profundus and follow the volar interosseous artery and nerve 

 to the point where they disappear behind the pronator quadratus 

 in the distal third of the forearm. Clean the pronator quadratus, 

 then proceed to study the structures exposed. 



Arteria Ulnaris. The ulnar artery is the larger of the 

 two terminal branches of the brachial trunk. It takes origin, 

 in the cubital fossa, at the level of the neck of the radius. In 

 the proximal third of the forearm it inclines obliquely distally 

 and medially, and then it proceeds straight down to the 

 wrist. It enters the palm by passing anterior to the transverse 

 carpal ligament. In the proximal oblique portion of its course 

 the vessel is deeply placed, and is crossed by both heads of the 

 pronator teres, the flexor carpi radialis, the palmaris longus, 

 the flexor digitorum sublimis and the median nerve. Its distal, 

 vertical part is overlapped on the medial side by the flexor 

 carpi ulnaris, but a short distance proximal to the wrist it 

 becomes superficial, and lies in the interval between the 

 tendon of the flexor carpi ulnaris on the medial side and the 

 tendons of the flexor sublimis on the lateral side. As it lies 

 on the transverse carpal ligament it is separated from the 

 lateral side of the pisiform bone by the ulnar nerve, and is 

 covered by a strong band of fascia, the volar carpal ligament 

 (pp. 129, 162), which lies superficial to the transverse liga- 

 ment. Throughout its entire course it is accompanied by 

 two vena comites. It has important relationships with the 

 median and ulnar nerves. The median nerve, which lies 

 upon its medial side at its origin, soon crosses it, but at 

 the point of crossing the nerve is separated from the artery 



