(C. 6, 7, 8, T. 1). The nerve arises from the lateral and medial cords by two heads, the medial of which passes superficially to the third part of the axillary artery to reach its lateral side. It descends in company with the brachial artery, crossing over (sometimes under) that vessel opposite the insertion of the coraco-brachialis, to lie medial to it at the elbow. The median enters the forearm between the two heads of the pronator radii teres, and then passes between the flexor sublimis digitorum and the flexor profundus digitorum, to appear at the wrist between the pal maris longus and the flexor carpi radialis, almost midway between the two styloid processes. It enters the palm beneath the anterior annular ligament, becomes expanded, and gives off its terminal branches. In the forearm the nerve is closely associated with the median branch of the anterior interosseous artery.
(1) Articular, to the elbow joint.
(2) Muscular, to the flexor carpi radialis, pronator radii teres, palmaris longus, and flexor sublimis digitorum.
(3) Anterior interosseous, accompanies the artery of the same name, and supplies the lateral half of the flexor profundus digitorum, the flexor longus pollicis, and pronator quadratus. It ends beneath the last-named muscle, giving off a small filament to the wrist joint.
(4) Palmar cutaneous, pierces the deep fascia in the lower part of the forearm, and passes over the anterior annular ligament to be distributed to the skin of the palm.
(5) Terminal. There are two terminal branches, a lateral and a medial. The former innervates the abductor, opponens, and lateral head of the flexor brevis pollicis, subsequently giving off three digital branches. The first digital runs along the lateral border of the thumb; the second along its medial border, and the third along the lateral border of the index finger. A small twig passes from the third digital to the first lumbrical muscle. The medial branch furnishes the fourth and fifth digital nerves. The fourth supplies the second lumbrical, and then divides into branches for the contiguous sides of the index and middle fingers. The fifth digital is distributed to the adjacent sides of the middle and ring fingers. It communicates with the ulnar and frequently sends a small twig to the third lumbrical. The digital nerves give off branches to both the front and the back of the fingers, and in addition supply the interphalangeal joints.
In the palm the digital nerves lie under cover of the superficial palmar arch, but on the fingers they are anterior to the digital vessels.