THE ULNAR ARTERY 577 



beneath the pronator teres and superficial flexor muscles, and, having reached the 

 ulnar side of the arm about midway between the elbow and the wrist, it passes 

 directly downward, being merely overlapped by the flexor carpi ulnaris. Crossing 

 the transverse carpal (anterior annular) ligament immediately to the radial side 

 of the pisiform bone, it enters the palm, where it divides into two branches, which 

 enter respectively into the formation of the superficial and deep volar arches. 

 The artery is accompanied by two veins, which anastomose with each other by 

 frequent cross branches, and usualty terminate in the brachial vense comitantes. 

 The ulnar nerve is at first some distance from the artery, but approaches the 

 vessel at the junction of its upper and middle thirds, and then lies close to its 

 medial or ulnar side. The course of the artery- in the lower two-thirds of the 

 forearm is indicated by a line drawn from the front of the medial epicondyle to 

 the radial side of the pisiform bone; and in the upper third of the forearm by a 

 line drawn in a gentle curve with its convexity to the medial side from 2.5 cm. 

 (1 in.) below the centre of the bend of the elbow to a point in the former line at 

 the junction of its upper with its middle third. The artery throughout its course 

 is best reached through the interval between the flexor carpi ulnaris and the 

 flexor digitorum sublimis. 



The relations of the artery will be given in detail in the forearm, and in the palm of the 

 hand. 



The relations in the forearm are : — 



In front. — -In the upper half of the forearm the ulnar artery is deeply placed beneath the 

 pronator teres, the flexor carpi radiahs, the palmaris longus, and the flexor digitorum sublimis. 

 In the lower half it is comparatively superficial, being merely overlapped above by the tendon 

 of the flexor carpi ulnaris, whilst the last inch or so of the vessel is only covered as a rule by 

 the skin and superficial and deep fascijB. As the artery lies beneath the pronator teres, it is 

 crossed from the medial to the lateral side by the median nerve, the deep head of origin of the 

 muscle usually separating the nerve from the artery. The lower part of the artery is crossed 

 by the palmar cutaneous branch of the ulnar nerve. 



Behind. — For about 2.5 cm. (1 in.) of its course the artery Mes upon the brachialis; but 

 thence, as far as the transverse carpal (anterior annular) ligament, upon the flexor digitorum 

 profundus, which separates it above from the interosseous membrane and bone, and at the 

 wrist from the pronator quadratus. The artery is bound down to the flexor digitorum pro- 

 fundus bj- bands of fascise. 



To the lateral side in the lower two-thirds of its course is the flexor digitorum sublimis. 



To the medial side in the lower two-thirds is the flexor carpi ulnaris, the guide to the 

 vessel. The ulnar nerve, as it enters the forearm from behind the medial epicondyle, is at first 

 some distance from the artery, being separated from it in its upper third by the flexor digitorum 

 sublimis, but in its lower two-thirds is in close contact with the vessel and on its ulnar side. 



The branches of the ulnar artery in the forearm are: — 1. The ulnar recurrent 

 arteries. 2. The common interosseous. 3. Muscular. 4. Dorsal ulnar carpal. 

 5. Volar ulnar carpal. 



1. The ulnar recurrent arteries [aa. recurrentes ulnares] are two, the volar, and dorsal. 

 The volar is a small branch which arises from the medial side of the ulnar artery, or the dorsal 

 ulnar recurrent, and, running between the lateral edge of the pronator teres and the brachiahs. 

 anastomoses in front of the medial epicondyle with the inferior and superior ulnar collaterals. 

 It supplies branches to the muscles between which it runs, and to the skin. The dorsal, larger 

 than the volar, comes'ofi' from the medial side of the ulnar artery, either a little below the latter 

 branch, or else as a common trunk with it, and, passing between the flexores digitorum sublimis 

 and profundus, turns upward to the back of the medial epicondyle, where it lies with the ulnar 

 nerve between the two heads of origin of the flexor carpi ulnaris. It supphes the contiguous 

 muscles — the flexor carpi ulnaris, the palmaris longus, and the flexores digitorum sublimis and 

 profundus — the elbow-joint, and the ulnar nerve, and anastomoses with the inferior and superior 

 ulnar collaterals, and with the interosseous recurrent forming the so-called rete olecrani. 



2. The common interosseous artery [a. interossea communis] is a short thick 

 trunk 1.2 cm. (| in.) or so in length, which comes off from the lateral and back 

 part of the ulnar artery about 2.5 cm. ( 1 in.) from its origin, and just before 

 that artery is crossed by the median nerve. It passes backward and downward 

 between the flexor poUicis longus and the flexor digitorum profundus, toward the 

 triangular interval bounded by the upper border of the interosseous membrane, 

 the oblique ligament, and the lateral border of the ulna, where it divides into the 

 volar and dorsal interosseous arteries. 



(a) The volar interosseous artery [a. interossea volaris], smaller than the dorsal, but 

 apparently the direct continuation of the common trunk, courses downward in front of the 

 interosseous membrane. It lies under cover of the overlapping edges of the flexor digitorum 

 profundus and flexor pollicis longus, to both of which muscles it supphes branches. At the 



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