The radial nerve (C5 - C8, T1) starts positioned behind the axillary artery. It enters the upper arm and gives off the following branches:

Muscular branches - innervate the triceps brachii and anconeus muscles
Posterior cutaneous nerve of the arm - innervates the skin of the posterior side of the upper arm.

After crossing the lateral epicondyle of the humerus, the nerve terminates by dividing into two terminal branches:

Superficial branch - travels down the forearm and, after looping under the tendon of the brachioradialis, enters the dorsal side of the hand. Then it branches into five dorsal digital nerves. These innervate the skin on the radial side of the dorsal hand, at the level of the proximal phalanx of the first and second finger, as well as the radial part of the proximal phalanx of the third finger.
Deep branch - penetrates the supinator muscle and gives off muscular branches. The muscular branches innervate the posterior and lateral muscles of the forearm. The deep branch also gives rise to the posterior cutaneous nerve of the forearm that innervates the skin on the posterior side of the forearm. The terminal part of the deep branch gives rise to the posterior interosseous nerve. It descends the interosseous membrane posteriorly and gives off muscular branches that innervate the deep layer of the posterior forearm muscles, and articular branches that innervate palm joints on the radial side.

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Radial nerve