Flexor Carpi Radialis Muscle Origin: Medial epicondyle of humerus, via common flexor tendon. Insertion: Palmar aspects of bases of second and third metacarpal bones. Action: Flexes hand at radiocarpal (wrist) joint; abducts hand at radiocarpal and midcarpal joints. Innervation: Median nerve (C6-C7). The common flexor tendon is the combined tendon for all five superficial muscles in the anterior compartment of the forearm, which are the: - pronator teres muscle; - flexor carpi radialis muscle; -