DIGITAL BRANCHES. -PECULIARITIES. 399 



lower down than the preceding, and, sending branches to the abductor 

 iudicis, runs along the radial side of the back of the index finger. 



c. The branches derived from the radial after it has entered the hand, 

 are the great artery of the thumb, the radial branch of the index finger, 

 and its large terminal branch, which forms the deep palmar arch. 



(a) The larye artery of the thumb (arteria princeps pollicis, Haller) arises 

 from the radial, where it is about to turn inwards across the palm of the 

 hand. It descends in front of the abductor iudicis, between the raetacarpal 

 bone of the thumb and the muscles covering it, to the space between the 

 lower ends of the dexor brevis pollicK At that point, and beneath the 

 tendon of the long flexor, it divides into two collateral branches, which 

 course along the borders of the phalanges, on the palmar aspect, and unite 

 in front of the last phalanx, to form an arch similar in arrangement to that 

 on the other fingers. 



(6) The radial branch for the index finger generally arises close to the 

 large artery of the thumb ; but, though constantly found, it varies in size 

 and in its mode of origin. It descends between the abductor iudicis and 

 adductor pollicis muscles, and continues along the radial border of the index 

 finger, forming the racial collateral branch of that finger, and anastomosing 

 in the usual manner on the last phalanx with the ulnar collateral branch 

 derived from the superficial palmar arch. 



This artery very frequently gives off a communicating branch to the superficial 

 arch, near the lower border of the adductor pollicis. But the most frequent com- 

 munication between the radial artery and the superficial arch is by means of the small 

 branch which proceeds from the former through the muscles of the thumb. 



PECULIARITIES. Origin. In the observations of Richard Quain, the radial artery 

 was found to arise higher up than usual in nearly one case in eight. 



Course.- The radial artery more rarely deviates from its usual position along the 

 fore arm than the ulnar. It has, however, been found lying upon the fibrous expan- 

 sion from the tendon of the biceps, and over the fascia of the fore -arm, instead of 

 beneath those structures. This vessel has been also observed on the surface of the 

 long supinator, instead of on the inner border of that muscle. In turning round the 

 wrist, it has been seen passing over the extensor tendons of the thumb, instead of 

 within them. But these several peculiarities are of very rare occurrence. As was 

 previously stated (p. 387), the vasa aberrantia occasionally derived from the bra- 

 chial or axillary arteries most commonly end by joining the radial, or one of its 

 branches. 



Brandies. The radial recurrent is sometimes very large, or it may be replaced 

 by several separate branches. When the radial itself arUes high up, the recurrent 

 artery usually comes from the residual brachial trunk, or sometimes from the 

 ulnar artery, or more rarely from the interosseous. When given from the brachial 

 trunk, the radial recurrent has been found crossing beneath the tendon of the 

 biceps. 



The superficial volar branch is small in a considerable number of cases, and is lost 

 in the short muscles of the thumb, without forming any connection with the palmar 

 arch, or with any of the digital arteries. 



In some instances in which it is enlarged, it furnishes one or two digital branches, 

 and along with this the anastomosis with the superficial arch may be absent. The 

 superficial volar branch occasionally arises as much as an inch and a half higher than 

 usual. 



The first dorsal interosseous branch (metacarpal), which descends on the second 

 interosseous space to the cleft between the index and middle fingers, is not unfre- 

 quently so large as to furnish the collateral digital branch to each of those fingers. 



The carpal and interosseous (metacarpal) branches of the radial are sometimes 

 small, their place being supplied by the perforating offset of the anterior interosseous, 

 apparently by an enlargement of the ordinary anastomosis between them. 



