i8o THE SUPERIOR EXTREMITY 



radial extensor of the wrist helps to extend and abduct the 

 hand at the wrist-joint, and it assists in flexion of the elbow 

 (Figs. 74, 75, 76). 



M. Extensor Carpi Radialis Brevis. The extensor carpi 

 radialis brevis is closely associated with the preceding muscle. 

 It arises, by the common extensor tendon, from the lateral 

 epicondyle of the humerus ; it derives fibres also from the 

 radial collateral ligament of the elbow-joint, from the in- 

 vesting deep fascia, and the fibrous septa in connection 

 with it. The tendon of the muscle accompanies that of 

 the long radial extensor under cover of the dorsal carpal 

 ligament, and is inserted into the dorsal aspect of the base 

 of the third metacarpal bone, immediately beyond the root 

 of its styloid process. This muscle is supplied by the deep 

 branch of the radial nerve by a twig given off before the nerve 

 pierces the supinator muscle. It is an extensor of the wrist 

 and the elbow, and an abductor of the hand at the wrist-joint. 



M. Extensor Digitorum Communis. The extensor digi- 

 torum communis takes origin, by the common tendon, 

 from the lateral epicondyle of the humerus. The deep 

 fascia and the intermuscular septa in relation to it also 

 contribute fibres. Its fleshy belly, in the distal part of the 

 forearm, ends in four tendons, which pass under cover of 

 the dorsal carpal ligament. On the dorsum of the hand 

 they diverge and proceed onwards to the four fingers. Their 

 arrangement and attachments on the dorsum of the hand and 

 fingers have already been considered (p. 177). The muscle is 

 supplied by the dorsal interosseous nerve. It is an extensor of 

 all the joints of the fingers, of the wrist, and of the elbow. 



M. Extensor Digit! Quinti Proprius (O.T. Extensor 

 Minimi Digiti). The extensor digiti quinti proprius is a 

 slender fleshy belly which at first sight appears to be a part of 

 the preceding muscle, but its tendon passes through a special 

 compartment in the dorsal carpal ligament. It arises in 

 common with the extensor digitorum communis. Its tendon 

 of insertion splits into two parts. The lateral of the two 

 joins the tendon of the extensor digitorum communis, which 

 passes to the little finger, and the medial part ends in the 

 extensor expansion on the dorsum of the first phalanx of the 

 little finger. The muscle is supplied by the dorsal interosseous 

 nerve. It is an extensor of all the joints of the little finger, 

 and it aids in extension of the wrist and elbow. 



