Of these branches the radial recurrent is sometimes very large, or it may be represented by several separate branches. When the radial itself arises high up, the recurrent artery usually comes from the residual brachial trunk or 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 of the radial was found, in a large proportion of cases examined, 141 in 235, to be small, and to be lost in the short muscles of the thumb, without forming any connection with the palmar arch, or, with any of the digital arteries. When the superficial volar had considerable size, its disposition varied as follows. In the majority of cases it simply ended in the superficial arch. In a smaller number, without joining the ulnar portion of the arch, it furnished one or more digital arteries. Lastly, the artery at the same time joined the arch, and furnished one or more digital branches to the thumb and index-finger.
The origin of the branch in question was also found to present some peculiarities. It occasionally arose from the radial at a distance of one inch and a half to two inches and a half above its ordinary position, in one case even nearly as high as the bend of the elbow. In these cases it usually descended with the radial ; but when the latter turned outwards to reach the back of the limb sooner than usual, the superficial volar occupied the place of the radial in front.
The first dorsal interosseous branch (metacarpal), which descends on the second interosseous space to the cleft between the index and middle fingers, is not infrequently 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 division of the anterior interosseous, apparently by an enlargement of the ordinary anastomosis between them.
Palmar branches of the radial artery
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.
The large artery of the thumb (arteria pollicaris: ar. 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 indicis, along the metacarpal bone of the thumb to its lower end (comes ossis metacarpi pollicis, — Haller), between the bone and the short muscles covering it, to the space between the lower ends of. the short flexor of the thumb. At that point, and beneath the tendon of the long flexor, the artery divides into two branches, the collateral arteries of the thumb, which course along the borders of its phalanges on their palmar aspect, and inosculate on the last phalanx, forming an arch similar in its arrangement to that on the other fingers.
The radial branch for the index-finger (art. volaris radialis indicis, — Haller), generally arises close to the preceding branch ; but though constantly found, it varies in size and in its mode of origin. It descends at first between the abductor indicis, which is behind it, and the flexor brevis and adductor pollicis in front; and continues, covered only by the skin and fascia, along the radial border of the index-finger, forming its radial collateral branch (whence its name), and anastomosing in the usual manner with the ulnar collateral branch for the same finger, derived from the superficial palmar arch. This artery very frequently gives a communicating branch to the superficial arch, near the lower border of the adductor pollicis.
The most frequent method of communication between the radial artery and the superficial arch is by a small branch, which proceeds from the former through the muscles of the thumb.
Deep palmar arch
The deep palmar arch (arcus profundus volae, — Haller), which is to be regarded as the palmar continuation of the radial artery, commences at the upper end of the first interosseous space, between the heads of the abductor indicis, turns transversely across the palm towards the upper end of the fourth metacarpal bone, near which it inosculates with the communicating branch from the ulnar artery, arid thus forms the deep palmar arch. The convexity of this arch is directed downwards. It is, as its name implies, more deeply seated than the superficial arch derived from the ulnar artery, — being placed upon the interosseous muscles, and the metacarpal bones, immediately below the carpal extremities of these; and being covered by the flexor brevis pollicis, the flexor tendons of the fingers, the lumbricales muscles, and the muscles of the little finger. It is also higher or nearer to the carpus than the superficial arch, and differs from it in retaining its size almost undiminished. It is accompanied by the deep branch of the ulnar nerve, which runs from the inner end of the arch outwards.
The deep palmar arch gives off recurrent branches (rami retrogradi, — Haller) from its upper concave side, which ascend and anastomose with the branches from the anterior carpal arch. It likewise furnishes superior perforating branches, three in number, which pass backwards through the upper extremities of the last three interosseous spaces to inosculate with the dorsal interosseous arteries. Lastly, the deep palmar arch affords origin, from its convexity, to the palmar interosseous arteries (interosseae volares, — Haller), usually three in number, but very liable to variation, which lie upon the interosseous spaces, supply the muscles there, and anastomose at the clefts of the fingers with the digital branches from the superficial arch. It is by an enlargement of these small vessels that the deep palmar arch sometimes supplies the corresponding digital arteries in the absence of those usually derived from the superficial arch.
From Quain's Anatomy.