1056 THE VASCULAR SYSTEM. 



radial and ulnar, whilst the other is the interosseous artery. Occasionally the brachial artery 

 terminates by dividing into three branches viz., the radial, the ulnar, and the interosseous. 

 In any case, the branch which gives origin to or becomes the interosseous was, in all probability, 

 the original trunk. 



Division of the brachial artery at a more proximal level than usual occurs most commonly in 

 the proximal third of the arm, and least commonly in the distal third ; the resulting trunks 

 are often united near the bend of the elbow by a more or less oblique anastomosis. 



In cases of proximal division of the brachial artery the radial branch may pierce the deep 

 fascia of the arm near the bend of the elbow, and passes distally in the forearm immediately deep 

 to the skin ; in other cases the radial runs deeper, and passes behind the tendon of the biceps. The 

 ulnar branch sometimes runs, on the medial intermuscular septum, towards the medial epicondyle, 

 and then laterally towards the middle of the bend of the elbow, under a band of fascia from 

 which the proximal fibres of the pronator teres arise, or round the supracondylar process of the 

 humerus if it is present. More commonly the ulnar branch runs distally towards the medial 

 epicondyle, and crosses superficial to the flexor muscles or deep to the palmaris longus ; and in 

 a few cases it is subcutaneous. In rare cases the ulnar artery accompanies the ulnar nerve 

 behind the medial epicondyle ; in those cases it has obviously been formed by enlargement 

 of the ordinary superior ulnar collateral and dorsal ulnar recurrent arteries. 



Instead of following its usual course along the brachialis muscle, the brachial artery may 

 accompany 'the median nerve behind a supracondylar or epicondylic process, or ligament, as in 

 many carnivora ; it may pass in front of the median nerve instead of behind it. It may give 

 off a " vas aberrans " or a median artery, and any of its ordinary branches may be absent. 



The vas aberrans given off from the brachial artery usually ends in the radial artery, some- 

 times in the radial recurrent, and rarely in the ulnar artery. 



The ulnar artery may be absent, being replaced by the median artery or the inter- 

 osseous artery, and it may terminate in the deep instead of in the superficial volar arch. It 

 rarely arises more distally than usual, and when it arises at a more proximal point it most 

 commonly passes superficial to the muscles which spring from the medial epicondyle. Moreover, 

 in those cases it frequently has no interosseous branch, the latter vessel springing from the radial 

 artery, and in all probability variations of this description are produced by the ulnar artery 

 taking origin from the main trunk, which is represented by the radio-interosseous vessel, at a 

 more proximal level than usual Even when it commences in the usual way the ulnar artery 

 may pass superficial to the muscles arising from the medial epicondyle, and in those cases its 

 interosseous and recurrent branches spring from the radial artery. 



The volar and dorsal interosseous arteries may arise separately from the ulnar instead of; 

 by a common interosseous trunk. The recurrent branches of the ulnar may spring from the 

 interosseous, and the interosseous itself may be a branch of the radial. 



The small median artery, the companion artery of the median nerve, usually a branch of the 

 volar interosseous, may spring from the axillary, brachial, or ulnar arteries ; it may be much 

 larger than usual, and it may terminate either by breaking up into digital branches, or by j 

 joining one or more digital branches of the superficial volar arch or the arch itself. 



The radial artery may be absent, its place being taken by branches of the ulnar or inter- 

 osseous arteries ; it may arise, more proximal than usual, from the axillary, or from the bracliial. 

 It may terminate in muscular branches in the volar part of the forearm, or as the superficial 

 volar, or in carpal branches ; the distal portion of the artery, in those cases, is usually replaced 

 by branches of the ulnar or interosseous arteries. Occasionally the radial divides some distance 

 proximal to the wrist into two terminal branches, one of which gives off the carpal branches, 

 and becomes the superficial volar, whilst the other crosses superficial to the extensor tendons 

 and passes to the dorsum of the wrist. 



The radial artery may run a superficial course, or, and especially when it commences at a 

 more distal level than usual, it may pass deep to the pronator teres and the radial origin of thej 

 flexor digitorum sublimis. In some cases it passes to the dorsum of the wrist across the brachio-a 

 radialis, and in others it lies superficial, instead of deep to, the extensor tendons of the thumb. 



Its branches may be diminished or increased in number. The radial recurrent may spring 

 from the brachial or ulnar arteries, or may be represented by several branches from the proxima 

 part of the radial. The dorsal artery of the index digit may be large, and may replace th<| 

 princeps pollicis and the volaris indicis radialis. On the contrary, the dorsal carpal artery anc 

 dorsal digital branches of the radial may be small, or the former may be replaced by branches o j-i 

 the metacarpal arteries, and the latter by the proximal perforating branches of the deep volar arch j 



The princeps pollicis and volaris indicis radialis arteries may be absent, their places bein^ 

 taken either by branches of the superficial volar arch or by the dorsalis indicis radialis artery. 



The superficial volar arch is sometimes absent ; its branches are then given off from the dee- 

 arch. On the other hand, it may be larger than normal, and it may be completed on the radia 

 side by the volaris indicis radialis, the princeps pollicis, or the comes nervi median! arteries. 



The deep volar arch is much more rarely absent than the superficial arch. When absen 

 its branches are supplied by the superficial arch, the proximal perforating arteries, or the vola 

 carpal arch. 



THE ILIAC ARTERIES AND THEIR BRANCHES. 



The common iliac artery may be longer or shorter than usual, a modification which 

 determined largely, though not altogether, by the point at which the bifurcation of the aorl; 



