Median nerve arises by two roots-one from the outer cord and one from the inner. The outer head passes down on the outer side of the axillary artery, and the inner head crosses over at the beginning of the brachial artery to join it. The complete nerve then passes down on the outer side of the brachial artery, and crosses over it to the inner side, at the level of the inferior profunda branch about the middle of the arm. At the elbow it lies on the inner side of the artery beneath the bicipital fascia and the median basilic vein, and passes into the forearm between the two heads of pronator radii teres, the deep head of which separates the nerve from the ulnar artery. The nerve then passes down the forearm between the superficial and deep muscles, and enters the palm of the hand beneath the anterior annular ligament on the outer side of the flexor tendons. In the hand it lies beneath the palmar fascia and superficial palmar arch, and divides into its six terminal branches.

Branches

There are none in the upper arm.

In the forearm:

1. Articular to the elbow-joint.

2. Muscular to pronator radii teres, palmaris longus, flexor carpi radialis, flexor sublimis digitorum, flexor longus pollicis, and flexor profundus digitorum.

3. Anterior Interosseous passes down the anterior surface of interosseous membrane with the artery of the same name and beneath the pronator quadratus. It terminates by supplying the wrist-joint, and in its course supplies flexor longus pollicis, outer half of flexor profundus digitorum, pronator quadratus, and twigs to the bones, periosteum, and interosseous membrane.

4. Palmar Cutaneous branch (not always present) arises in the lower third of the forearm, pierces the deep fascia, and supplies the skin of the palm.

In the hand: 1. Muscular to abductor pollicis, opponens pollicis, superficial head of flexor brevis pollicis, and the two lumbricales on the radial side.

2. Cutaneous to the skin of the thumb, the first and second fingers, and the radial half of the third finger. These nerves turn over the tops of the fingers and supply the posterior surface of the terminal phalanges.