902 THE VASCULAR SYSTEM. 
Instead of following its usual course along the brachialis anticus, the brachial artery may 
accompany the median nerve behind a supracondylar or epicondylic process, or ligament, as in 
many carnivores ; 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 “comes nervi mediani” or the inter- 
osseous artery, and it may terminate in the deep instead of in the superficial palmar arch. It 
rarely rises at a lower level than usual, and when it rises at a higher level it most commonly 
passes superficial to the muscles which spring from the internal epicondyle. Moreover, in these 
cases 1t 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 higher 
level than usual. Even when it commences in the usual way the ulnar artery may pass super- 
ficial to the muscles from the internal epicondyle, and in these cases its interosseous and recurrent 
branches spring from the radial artery. 
The anterior and posterior 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 
anterior interosseous, may spring from the axillary, brachial, or ulnar arteries; it may be much 
larger than usual, and terminate either by breaking up into digital branches, or by joining one 
or more digital branches of the superficial palmar arch or the palmar arch itself. 
The radial artery may be absent, its place being taken by branches of the ulnar or inter- 
osseous arteries ; it may arise from the axillary, or, higher than usual, from the brachial. It may 
terminate in muscular branches in the front of the forearm, or in the superficialis vole, or in 
carpal branches; the lower portion of the artery, in these cases, is usually replaced by branches 
of the ulnar or interosseous arteries. Occasionally the radial divides some distance above the 
wrist into two terminal branches, one of which gives off the carpal branches, and becomes the 
superficialis vole, whilst the other crosses superficial to the extensor tendons and passes to the 
back of the wrist. 
The radial artery may run a superficial course, or, and especially when it commences at a 
lower level than usual, it may pass beneath the pronator radii teres and the radial origin of the 
flexor sublimis digitorum. In some cases it passes to the back of the wrist across the supinator 
longus, and in others it lies upon, instead of beneath, 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 upper 
part of the radial. The dorsalis indicis may be large, and may replace the princeps pollicis and the 
radialis indicis. On the contrary, the dorsal carpal artery and dorsal digital branches of the 
radial may be small, or the former may be replaced by branches of the interosseous arteries, and 
the latter by the superior perforating branches of the deep palmar arch. 
The princeps pollicis and radialis indicis arteries may be absent, their places being taken 
either by branches of the superficial palmar arch or by the dorsalis indicis artery 
The superficial palmar arch is sometimes absent ; its branches are then given off from the 
deep arch. Conversely, it may be larger than normal, and it may be completed on the ulnar side 
by the radialis indicis, the princeps pollicis, or the comes nervi mediani arteries. 
The deep palmar arch is much more rarely absent than the superficial arch. When absent 
its branches are supplied by the superficial arch, the superior perforating arteries, or the palmar 
carpal arch. 
THE ILIAC ARTERIES AND THEIR BRANCHES. 
The common iliac artery may be longer or shorter than usual, a modification which is 
largely though not altogether determined by the point at which the bifurcation of the aorta takes 
place. If exceptionally long, it is usually tortuous. In rare cases in man the artery isabsent. It 
occasionally gives off the middle or a lateral sacral artery, and ilio-lumbar, spermatic, or 
accessory renal branches may arise from it. : f 
The internal iliac artery varies as regards length. It is usually longer, and rises at a higher 
level when the common iliac is short. In rare cases it has been found to arise from the aorta 
without the intervention of a common iliac. Frequently it does not, even in appearance, end in 
anterior and posterior divisions, but obviously forms a single trunk, as in the foetus, from which 
the several branches are given off. i 
The visceral branches vary much in number and size, and the middle hemorrhoidal may not 
be present, its place being taken by branches from the vesical arteries. A renal branch some- 
times arises from the internal iliac. { 
The ilio-lumbar branch may rise from the common instead of from the internal iliac; the 
gluteal and sciatic may rise by a common stem, or the gluteal may be absent, and its place taken 
by a branch from the femoral artery ; the sciatic artery may, as in the foetus, constitute the main 
artery of the hind limb, and run down to become continuous with the popliteal artery. Probably 
the “comes nervi ischiadici” represents the original continuity of these two vessels. Occasionally 
the lateral sacral arteries do not arise from the internal iliac trunks. é 
In some few instances the obturator artery arises from the deep epigastric artery instead of 
from the internal iliac. The condition is apparently due to obliteration of the usual origin of 
