f. A. radialis ([Fig. 123]).—Distad of the convexity of the elbow the brachial artery takes the name radial artery. It passes from the supracondyloid foramen on the medial side of the biceps tendon (1) and beneath the pronator teres muscle (5), giving off small branches, as far as the middle of the forearm, where it gives off the ulnar artery (k). It then passes from beneath the pronator teres (5) and lies on the surface of the fifth part of the flexor profundus (8), covered only by the fascia and integument. Near the wrist it sends off a branch (m) toward the ulnar side of the arm, which passes into the palm on the surface of the tendon of the flexor profundus, giving twigs to the digits and to the pad in the palm. A branch from this may join the ulnar, and the common trunk thus formed passes into the hand and gives origin to the branches [described] under the ulnar artery. The presence and size of this branch of the radial varies with the size of the ulnar artery, it being smaller or absent as the ulnar is larger. It is shown at m, [Fig. 123]. The radial artery (g) now turns gradually dorsad and passes beneath the tendon of the extensor brevis pollicis onto the dorsum of the hand. It passes over the oblique groove on the dorsal surface of the base of the second metacarpal beneath the tendon of the extensor carpi radialis longus and passes between the bases of the second and third metacarpals into the palm of the hand. Here it passes to the ulnar side and anastomoses with the ulnar artery to form the palmar arch.

Branches of the Radial Artery.

1. A. radialis recurrens (i).—The radial recurrent arises in the concavity of the elbow and sends a branch proximad to the structures in the concavity; it then continues to the radial side of the forearm at the elbow, supplying adjacent parts of the brachialis (2), the extensor carpi radialis, and the extensor communis digitorum.

2. A. ulnaris recurrens (j).—The ulnar recurrent arises on the medial side of the tendon of the biceps and supplies structures in the concavity of the elbow on the ulnar side, also the pronator teres (5) and proximal ends of the flexor carpi radialis and flexor profundis digitorum.

3. Rami musculares.—Muscular branches are given off along the course of the artery, to adjacent muscles. A nutrient artery to the radius leaves the radial artery about two centimeters distad of the supracondyloid foramen.

4. Aa interosseæ (anterior (l) and posterior) are given off usually separately between the origin of the ulnar artery and the biceps tendon. Sometimes they arise as a common trunk which soon divides. The posterior interosseous artery passes distad, supplying the flexor muscles of the forearm. It also sends a branch to the pronator teres. The anterior interosseous (l) may arise from the ulnar artery. It passes dorsad to the interosseous membrane, on which it runs distad; sends a nutrient branch to the ulna, and then passes to the wrist in the substance of the pronator quadratus, which it supplies. It sends a branch to the dorsal surface of the wrist; this ramifies on the carpus, forming a network of small arteries.

[Fig. 123].—Nerves and Arteries of the Forearm, seen from the Flexor Side.

Mm. palmaris longus, flexor carpi radialis, flexor carpi ulnaris, and the third and fourth heads of flexor profundus digitorum have been removed; also part of M. pronator teres. 1, biceps; 2, conjoined tendon of brachialis and clavobrachialis; 3, short portion of caput mediale of triceps brachii; 4, intermediate portion of caput mediale of triceps brachii; 5, cut ends of pronator teres; 6, brachioradialis; 7, extensor carpi radialis longus and brevis; 8, fifth head of flexor profundus digitorum; 9, second head of flexor profundus digitorum; 10, radial part of flexor sublimis digitorum; 11, common tendon of flexor profundus digitorum; 12, first head of flexor profundus digitorum; 13, cut origin of flexor carpi ulnaris. a, ulnar nerve; b, median nerve; c, dorsal cutaneous branch of the ulnar nerve; d, palmar branch of ulnar nerve; e, deep palmar branch; f, superficial palmar branch; g′, A. brachialis; g, A. radialis; h, A. collateralis ulnaris superior; i, A. radialis recurrens; j, A. ulnaris recurrens; k, A. ulnaris; l, A. interossea anterior; m, large branch of A. radialis, joining A. ulnaris.

5. A. ulnaris (k).—The ulnar artery passes beneath the second, third, and fourth parts of the flexor profundus digitorum (but outside of the origin of the fifth part), to the inner surface of the flexor carpi ulnaris. It supplies the flexor carpi ulnaris, the flexor profundus and palmaris longus, and passes on the inner surface of the flexor carpi ulnaris to the wrist. Near the wrist it sends a branch onto the side of the forearm, and another to its midventral part, and ends in a small branch to the wrist on the radial side of the pisiform bone. This branch anastomoses with the radial to form the palmar arch, described below.