Action.—Extensor of the hand.
M. extensor carpi radialis brevis ([Fig. 77], p).—A slender muscle from the humerus to the third metacarpal.
Origin ([Fig. 81], l) from the distal part of the lateral supracondyloid ridge distad of the extensor longus. Near the carpus the muscle ends in a slender tendon which passes through the groove with the extensor longus tendon. The tendon then diverges from the extensor longus and has its
Insertion ([Fig. 84], f) into the radial side of the dorsal surface of the base of the third metacarpal.
Relations.—Outer surface with the extensor longus ([Fig. 77], o), the integument, and distad with the extensor pollicis brevis ([Fig. 84], d). Radial surface with the extensor longus. Ulnar surface with the extensor communis digitorum ([Fig. 75], m) and the extensor brevis pollicis. Inner surface with the pronator teres ([Fig. 77], q), supinator ([Fig. 85], b), and extensor brevis pollicis ([Fig. 85], a).
Action.—Extensor of the hand.
[Fig. 84].—Arrangement of the Tendons on the Back of the Hand.
![[Fig. 84]](#3418956513767812439_illo175lg.jpg.id-5867096379358212487.wrap-0.html.html){kind=link}
a, M. extensor communis digitorum; b, M. extensor lateralis digitorum; c, M. extensor indicis; d, M. extensor brevis pollicis; e, M. extensor carpi radialis longus; f, M. extensor carpi radialis brevis; g, M. extensor carpi ulnaris; h, tendons of the interossei. 1, transverse ligament of the wrist.
M. extensor digitorum communis ([Fig. 75], m).—A slender muscle from the lateral supracondyloid ridge of the humerus to the phalanges of the second, third, fourth, and fifth digits.