The ulnar nerve

The ulnar nerve (C(7), 8, T1; Fig. 142) is formed from the medial cord of the plexus. It lies medial to the axillary and brachial artery as far as the middle of the humerus, then pierces the medial intermuscular septum (in company with the superior ulnar collateral artery) to descend on the anterior face of triceps. It passes behind the medial epicondyle (where it can readily be rolled against the bone), to enter the forearm (Fig. 122). Here it descends beneath flexor carpi ulnaris until this muscle thins out into its tendon, leaving the nerve to lie superficially on its radial side. In the distal two-thirds of the forearm the nerve is accompanied by the ulnar artery which lies on the nerve's radial side. About 2 in (5 cm) above the wrist, a dorsal cutaneous branch passes deep to flexor carpi ulnaris to supply the dorsal aspects of the ulnar 1- fingers and the dorsal aspect or the ulnar side of the hand (Fig. 143).

The ulnar nerve crosses the flexor retinaculum superficially (Fig. 137) to break up into a superficial terminal branch, supplying the ulnar 1- fingers,

Trapezius

Pectoralis major

Brachial artery and vein

Pectoralis Major Nerve

Lateral and medial pectoral nerves

Lateral thoracic artery

Nerve to serratus anterior

Nerve to latissimus dorsi

Lower subscapular nerve

Ulnar nerve

Medial cutaneous nerve of arm

Fig. 142 Dissection of the upper arm to show the course of the major nerves.

Trapezius

Acromio-thoracic trunk Deltoid

Musculocutaneous nerve Cephalic vein

Pectoralis major

Medial cutaneous nerve of forearm

Brachial artery and vein

Lateral and medial pectoral nerves

Pectoralis minor Pectoralis major cut and turned back

Lateral thoracic artery

Nerve to serratus anterior

Nerve to latissimus dorsi

Lower subscapular nerve

Ulnar nerve

Medial cutaneous nerve of arm

Fig. 142 Dissection of the upper arm to show the course of the major nerves.

and a deep terminal branch which supplies the hypothenar muscles and the intrinsic muscles of the hand. Its branches are:

• muscular — to flexor carpi ulnaris, medial half of flexor digitorum profundus, the hypothenar muscles, the interossei, 3rd and 4th lumbricals and the adductor pollicis (i.e. it supplies all the intrinsic muscles of the hand apart from those of the thenar eminence and the 1st and 2nd lumbricals, which are innervated by the median nerve);

• cutaneous—to the ulnar side of both aspects of the hand and both surfaces of the ulnar 1-2 fingers.

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