All muscles of the deep layer are innervated by the posterior interosseous nerve, the continuation of the deep branch of the radial nerve.
The supinator muscle has two layers, which insert together on the proximal aspect of the radius (Fig. 7.91):
The more superficial (humeral) layer originates mainly from the lateral epicondyle of the humerus and the related anular ligament and the radial collateral ligament of the elbow joint.