Page 209 - Clinical Anatomy

ECA3 7/18/06 6:45 PM Page 194

194 The upper limb

supinator muscle then sprays out to be distributed to the extensor muscles
of the forearm.
The radial nerve itself continues as the superficial radial nerve, lying
deep to brachioradialis (Fig. 137). Above the wrist, it emerges posteriorly
from beneath this muscle to end by dividing into cutaneous nerves to the
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posterior aspects of the radial 3– digits.
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Branches
The radial nerve is the nerve of supply to the extensor aspect of the upper
limb. The main trunk itself innervates: triceps, anconeus, brachioradialis
and extensor carpi radialis longus. It also gives a twig to the lateral part of
brachialis.
The posterior interosseous branch supplies all the remaining extensor
muscles of the forearm together with the supinator and abductor pollicis
longus.
Cutaneous branches are distributed to the back of the arm, forearm and
radial side of the dorsum of the hand. So great is the overlap from adjacent
nerves, however, that division of the radial nerve results, surprisingly, in
only a small area of anaesthesia over the dorsum of the hand, in the web
between the thumb and index finger (Fig. 144a).

The musculocutaneous nerve

The musculocutaneous nerve (C5, 6, 7) continues on from the lateral cord of
the plexus. It pierces coracobrachialis then runs between biceps and
brachialis (supplying all these three muscles) to innervate, by its terminal
cutaneous branch, now termed the lateral cutaneous nerve of the forearm,
the skin of the lateral forearm.

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
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aspects of the ulnar 1– fingers and the dorsal aspect or the ulnar side of the
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hand (Fig. 143).
The ulnar nerve crosses the flexor retinaculum superficially (Fig. 137) to
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break up into a superficial terminal branch, supplying the ulnar 1– fingers,
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