Median nerve

The nerve is formed at the lower border of the axilla by the union of its medial and lateral roots, from the corresponding cords of the brachial plexus. The axillary artery is clasped between the two roots, the medial root crossing in front of the vessel. The commencement of the nerve is thus lateral to the artery. Passing distally through the arm the nerve lies in front of the brachial artery and at the elbow is found on its medial side. The nerve has no muscular branches in the arm (unless the nerve to pronator teres has an unusually high origin), but it gives sympathetic fila­ments to the brachial artery and a twig to the elbow joint.

The surface marking of the nerve is along a line from the medial bicipital groove behind coracobrachialis to the cubital fossa medial to the (palpable) brachial artery.

The median nerve, while still in the cubital fossa, gives a branch to pronator teres then disappears between the two heads of that muscle. Beyond the muscle it supplies flexor carpi radialis and palmaris longus, and then joins the ulnar artery at the fibrous arch of the superficial flexor. Deep to flexor digitorum superficialis it passes distally in the midline of the forearm closely attached by areolar tissue to the deep surface of the muscle, which it supplies. It emerges from the lateral border of the muscle, between palmaris longus and flexor carpi radialis tendons, and is slightly overlapped from the ulnar side by the tendon of palmaris longus before passing beneath the flexor retinaculum to enter the hand. At the wrist the nerve is not round but flattened. It is nour­ished by the median artery, a branch of the anterior interosseous which was the original axial artery of the fetal limb. It may persist as a large vessel. Small twigs from it on the surface of the nerve help at operation to distinguish the nerve from adjacent tendons.

The median nerve gives off an anterior interosseous branch which runs down with the artery of the same name and supplies flexor digitorum profundus (usually the bellies which move index and middle fingers), flexor pollicis longus and pronator quadratus, also the inter­osseous membrane and the periosteum of the radius and ulna. It ends in the anterior part of the capsule of the wrist joint and the carpal joints, which it supplies. It has no cutaneous branch.

Just above the flexor retinaculum the median nerve gives off a palmar branch to the skin over the thenar muscles.

The surface marking of the nerve is along a line from the point in the middle of the cubital fossa medial to the (palpable) brachial artery to a point at the wrist on the ulnar side of the tendon of flexor carpi radialis.