Henry Gray (18251861). Anatomy of the Human Body. 1918.
The volar branch (ramus volaris; anterior branch) descends along the radial border of the forearm to the wrist, and supplies the skin over the lateral half of its volar surface. At the wrist-joint it is placed in front of the radial artery, and some filaments, piercing the deep fascia, accompany that vessel to the dorsal surface of the carpus. The nerve then passes downward to the ball of the thumb, where it ends in cutaneous filaments. It communicates with the superficial branch of the radial nerve, and with the palmar cutaneous branch of the median nerve.
The dorsal branch (ramus dorsalis; posterior branch) descends, along the dorsal surface of the radial side of the forearm to the wrist. It supplies the skin of the lower two-thirds of the dorso-lateral surface of the forearm, communicating with the superficial branch of the radial nerve and the dorsal antibrachial cutaneous branch of the radial.
The musculocutaneous nerve presents frequent irregularities. It may adhere for some distance to the median and then pass outward, beneath the Biceps brachii, instead of through the Coracobrachialis. Some of the fibers of the median may run for some distance in the musculocutaneous and then leave it to join their proper trunk; less frequently the reverse is the case, and the median sends a branch to join the musculocutaneous. The nerve may pass under the Coracobrachialis or through the Biceps brachii. Occasionally it gives a filament to the Pronator teres, and it supplies the dorsal surface of the thumb when the superficial branch of the radial nerve is absent.
The Medial Antibrachial Cutaneous Nerve (n. cutaneus antibrachii medialis; internal cutaneous nerve) (Fig. 816)arises from the medial cord of the brachial plexus. It derives its fibers from the eighth cervical and first thoracic nerves, and at its commencement is placed medial to the axillary artery. It gives off, near the axilla, a filament, which pierces the fascia and supplies the integument covering the Biceps brachii, nearly as far as the elbow. The nerve then runs down the ulnar side of the arm medial to the brachial artery, pierces the deep fascia with the basilic vein, about the middle of the arm, and divides into a volar and an ulnar branch.
The volar branch (ramus volaris; anterior branch), the larger, passes usually in front of, but occasionally behind, the vena mediana cubiti (median basilic vein). It then descends on the front of the ulnar side of the forearm, distributing filaments to the skin as far as the wrist, and communicating with the palmar cutaneous branch of the ulnar nerve (Fig. 811).
The ulnar branch (ramus ulnaris; posterior branch) passes obliquely downward on the medial side of the basilic vein, in front of the medial epicondyle of the humerus, to the back of the forearm, and descends on its ulnar side as far as the wrist, distributing filaments to the skin. It communicates with the medial brachial cutaneous, the dorsal antibrachial cutaneous branch of the radial, and the dorsal branch of the ulnar (Fig. 813).
The Medial Brachial Cutaneous Nerve (n. cutaneus brachii medialis; lesser internal cutaneous nerve; nerve of Wrisberg) is distributed to the skin on the ulnar side of the arm (Figs. 811,813). It is the smallest branch of the brachial plexus, and arising from the medial cord receives its fibers from the eighth cervical and first thoracic nerves. It passes through the axilla, at first lying behind, and then medial to the axillary vein, and communicates with the intercostobrachial nerve. It descends along the medial side of the brachial artery to the middle of the arm, where it pierces the deep fascia, and is distributed to the skin of the back of the lower third of the arm, extending as far as the elbow, where some filaments are lost in the skin in front of the medial epicondyle, and others over the olecranon. It communicates with the ulnar branch of the medial antibrachial cutaneous nerve.
In some cases the medial brachial cutaneous and intercostobrachial are connected by two or three filaments, which form a plexus in the axilla. In other cases the intercostobrachial is of large size, and takes the place of the medial brachial cutaneous, receiving merely a filament of communication from the brachial plexus, which represents the latter nerve; in a few cases, this filament is wanting.