Identify the supinator muscle [probe]. It arises from the lateral epicondyle of the humerus, the crest of the ulna, and radial collateral and annular ligaments of the elbow joint. It inserts into the lateral aspect of the radius.
Note that it is pierced by the deep branch of the radial nerve [probe] which innervates it. The deep branch of the radial nerve then emerges from the posterior surface of the supinator muscle as the posterior interosseous nerve. The posterior interosseous nerve supplies the extensor muscles in the posterior compartment of the forearm.
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