Origin Lateral epicondyle of humerus, radial collateral and annular ligaments, supinator fossa and crest of ulna Insertion Lateral, posterior and anterior surfaces of proximal 1/3 of radius Action Supinates forearm (i.e., rotates radius to turn palm anteriorly) Innervation Deep branch of radial nerve (C5 and C6) (C5, C6) Arterial Supply Recurrent interosseous artery