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The ulnar artery, with its accompanying nerve, enters the hand superficial to the flexor retinaculum and to the radial side of the pisiform (see Plates 4-10 and 4-11). It descends, curving radially, to about the midpalm and there anastomoses with the superficial palmar branch of the radial artery. This branch passes across or through the muscles of the thenar eminence, supplies this group of muscles, and emerges medial to the eminence to help form the superficial palmar arterial arch. The arch is convex distalward and crosses the palm at the level of the line of the completely abducted thumb.

The branches of the superficial arch supply the medial three and one-half digits; the radial one and one-half digits are supplied from the deep palmar arterial arch. The superficial arch gives origin to three common palmar digital arteries, which proceed distalward on the flexor tendons and lumbrical muscles and superficial to the digital nerves of the palm. They unite at the webs of the fingers with the palmar metacarpal arteries and with distal perforating branches of the dorsal metacarpal arteries. From the short trunks thus formed spring proper palmar digital arteries.
Two proper palmar digital arteries run distalward along the adjacent margins of the second to fifth digits. A proper digital branch to the ulnar side of the fifth digit arises from the ulnar artery in the hypothenar compartment. At the webs of the fingers, the digital nerves cross the arteries to become superficial to them along the margins of the digits. Thus, in each digit, the palmar and dorsal digital arteries lie within the span of the corresponding cutaneous nerves. The proper palmar digital arteries anastomose to form terminal plexuses in the fingers. They also give off branches that supply the last two dorsal segments of the digits.

At the wrist, the radial artery shifts from the expanded palmar surface of the radius, through the floor of the anatomic snuffbox, to reach the dorsum of the hand at the proximal end of the first dorsal interosseous space. As it passes under the tendon of the abductor pollicis longus muscle, it gives origin to its dorsal carpal branch; continuing distally over the first dorsal interosseous space, it gives origin to the first dorsal metacarpal artery. (The radial artery then turns deeply into the palm of the hand and participates in forming the deep palmar arterial arch.) The dorsal carpal branch of the radial artery passes ulnarward across the distal row of carpal bones and under the extensor tendons and joins the dorsal carpal branch of the ulnar artery. Thus is formed the dorsal carpal arterial arch.
Three dorsal metacarpal arteries descend from this arch on the dorsal interosseous muscles of the second, third, and fourth intermetacarpal intervals, respectively. Opposite the heads of the metacarpals, these vessels divide into proper dorsal digital arteries, which proceed distally along the dorsal borders of contiguous digits. These vessels are small and fail to reach the distal phalanges of the digits. Anastomoses are formed between the dorsal metacarpal arteries and the palmar arterial system in two locations: by perforating branches at the bases of the metacarpals and at the division into proper dorsal digital arteries.
The deep palmar arterial arch is formed by the junction of the terminal portion of the radial artery and the deep branch of the ulnar artery. The radial artery enters the palm at the base of the first intermetacarpal space by penetrating between the two heads of origin of the first dorsal interosseous muscle. Passing then between the transverse and oblique heads of the adductor pollicis muscle, it joins the deep branch of the ulnar artery.
The princeps pollicis artery arises from the radial artery as it emerges from the first dorsal interosseous muscle. At the head of the first metacarpal, it provides two proper palmar digital branches for the thumb. The radialis indicis artery arises with the princeps pollicis to run along the radial side of the index finger. It is a proper digital artery to the radial side of the index finger.
From the convexity of the arch arise three palmar metacarpal arteries. These descend under the palmar interosseous fascia of the second to fourth intermetacarpal intervals. At the webs of the fingers, they join the common digital arteries from the superficial arch. Recurrent carpal branches are small. They ascend to and help form the palmar carpal network. Perforating branches anastomose with the dorsal metacarpal arteries on the dorsum of the hand.