Origin: Common extensor tendon (lateral epicondyle), ulna
Insertion: 5th metacarpal
Artery: Ulnar artery
Nerve: Posterior interosseous nerve (C7, C8)
Action: Extends and adductsthe wrist
Antagonist: Flexor carpi ulnaris
The Extensor carpi ulnaris lies on the ulnar side of the forearm. It arises from the lateral epicondyle of the humerus, by the common tendon; by an aponeurosis from the dorsal border of the ulna in common with the Flexor carpi ulnaris and the Flexor digitorum profundus; and from the deep fascia of the forearm. It ends in a tendon, which runs in a groove between the head and the styloid process of the ulna, passing through a separate compartment of the dorsal carpal ligament, and is inserted into the prominent tubercle on the ulnar side of the base of the fifth metacarpal bone.
Variations.—Doubling; reduction to tendinous band; insertion partially into fourth metacarpal. In many cases (52 per cent.) a slip is continued from the insertion of the tendon anteriorly over the Opponens digiti quinti, to the fascia covering that muscle, the metacarpal bone, the capsule of the metacarpophalangeal articulation, or the first phalanx of the little finger. This slip may be replaced by a muscular fasciculus arising from or near the pisiform.