Action.—Extensor of the four ulnar digits.
M. extensor carpi ulnaris ([Fig. 75], o).
Origin.—(1) By a short, broad tendon from the distal portion of the lateral epicondyle of the humerus ([Fig. 81], o) distad of the origin of the extensor lateralis, and (2) by a smaller tendon from the ulna at the dorsal tip of the semilunar notch ([Fig. 86], e).
The muscle passes along the ulnar side of the forearm dorsad of the extensor digitorum lateralis (n). It ends near the junction of the middle and distal thirds of the forearm in a large, flat tendon (o′) which is closely adherent to the ligaments of the wrist and which passes over the distal end of the ulna to its
Insertion into the tubercle on the ulnar side of the base of the fifth metacarpal ([Fig. 84], g).
Relations.—Outer surface with the integument. Radial (or ventral) border with the extensor digitorum lateralis ([Fig. 75], n); ulnar (or dorsal) border with the flexor profundus digitorum (q). Inner surface with the radius, the extensor indicis ([Fig. 85], c), and the extensor pollicis brevis ([Fig. 85], a).
Action.—Indicated by its name.
M. extensor indicis (proprius) ([Fig. 85], c; [Fig. 75], p) (includes extensor pollicis longus also).
Origin ([Fig. 86], f) by short, fleshy fibres from the lateral surface of the ulna between the semilunar notch and the junction of the third and fourth (distal) fourths.
The muscle-fibres pass obliquely distad and toward the radial side and join the tendon ([Fig. 85], c′), which runs nearly the whole length of the radial surface.