The Posterior Carpal Artery is very much larger than the anterior. Its origin corresponds to the outer edge of the extensor carpi radialis longus muscle, and is nearly opposite the interval between the first and second range of carpal bones. It passes almost horizontally inwards, lying on the second row of carpal bones, covered by the radial extensors and the extensors of the fingers, to anastomose with the posterior carpal branch of the ulnar artery; its superior branches are distributed to the wrist-joint, and communicate with the anterior interosseal; its inferior branches are the second, third, and fourth perforating arteries, each of which sinks between the heads of the corresponding dorsal interosseous muscle, to join the deep palmar arch: the trunk of the radial artery may be considered the first perforating artery, as it pierces the first interosseous muscle, or abductor indicis manus, in a similar manner. Before these arteries pierce the muscles, they send off interosseal branches, which descend between the interosseous muscles and integuments, and occasionally pierce the lower part of the interosseous space, to join the digital branches of the palmar arch.

Fig. 31. Represents the deep arteries of the posterior part of the upper extremity.

1, Humerus. 2, Brachialis Anticus. 3, Origins of Supinator Radii Longus and Extensor Carpi Radialis Longus Muscles. 4, Portion of Insertion of Triceps. 5, External Lateral Ligament of the Elbow-joint. 6, 6, Interosseous Ligament of the Fore-arm. 7, Ulna. 8, Radius, a, a, Superior Profunda Artery, b, Radial Recurrent Artery, o, c, Anastomoses between the Superior Profunda, the Radial Recurrent, and Interosseal Recurrent Arteries, d, Posterior Interosseal Artery, after passiug backwards between the Oblique and Interosseous Ligaments, divided, e, f, f, f, g, Perforating branches from the Anterior Interosseal Artery, b, Twig to Carpus, i, Radial Artery, k, k, k, Dorsal Carpal Twigs. 1, Dorsal Artery of Thumb, m, Internal Dorsal Artery of Thumb, n, Continuation of the Princeps Pollicis Artery, o, Radialis Indicis Artery, p, Posterior Carpal branch of Ulnar Arteryz, q, Branch of Posterior Ulnar Carpal Artery to the little finger, r, r, r, Perforating Twigs of the Palmar Interosseal Arteries, s, s, s. Dorsal or Posterior Interosseal Arteries of hand. t. Radial Artery passing into the palm of the hand, u, v, w, x, y, z, Small branches to the sides of the Dorsal aspect of the 1st, 2d, 3d, and 4th fingers.

The Dorsalis Pollicis

Before the radial artery sinks between the two first metacarpal bones, it gives a branch or branches to the posterior surface of the metacarpal bone of the thumb; it also frequently gives off a slender branch that descends on the cutaneous surface of the abductor indicis manus.

The Metacarpal Artery, Or Dorsalis Indicis

The Metacarpal Artery, Or Dorsalis Indicis, is very variable in size, being sometimes diminutive, and at other times extremely large. Sometimes it seems to be a continuation of the radial. It descends over the metacarpal bone of the index finger, and sinks between the second and third metacarpal bones, to join the digital branch of the superficial palmar arch that supplies the adjacent sides of the index and middle fingers.

The Radialis Indicis

The Radialis Indicis descends between the abductor indicis and adductor pollicis : it then follows the external margin of the index finger, and, at its extremity, anastomoses with the internal digital branch of the same finger.