MUSCLES OF THE THOR/iClC LIMBS. 



175 



through the groove on the middle of the dorsal surface of the 

 distal end of the radius. The groove is converted into a canal 

 by a strong transverse ligament. The 

 tendon divides near the groove into four 

 portions (Fig. 84, a) which diverge and 

 pass to the four ulnar digits. 



Insertions. — Each division of the 

 tendon as it passes over the dorsal sur- 

 face of the first phalanx has its border 

 connected by strong fascia to the dorsal 

 surface of the phalanx. It finally passes 

 through the groove at the distal end of 

 the first phalanx and is inserted mostly 

 into the base of the second phalanx ; a 

 portion continues distad to be inserted 

 into the third phalanx. 



Relations. — Outer surface with the 

 integument and at the origin with the 

 caput laterale (Fig. 75, //) of the triceps. 

 Radial surface with the extensor longus 

 (/) and extensor brevis. Ulnar surface 

 with the extensor digitorum lateralis {11). 

 Inner surface with the supinator (Fig. 

 85, li) a'nd the extensor poUicis brevis 

 (Fig. 85, a). ^ 



Action. — Extensor of the four ulnar 

 digits. 



M. extensor digitorum lateralis 

 (Fig. 75,;/). (This corresponds in posi- '"-'^''■^ ^I'S'torum; c. 



. ...... . sor indicis; </, M 



Fig. 84. — Arrangement of 

 THE Tendons on the 

 Back of the Hand. 



(I, M. extensor communis 



digitorum; h, M. extensor late- 



M. exten- 



^..,, -, M. extensor 



tion to the extensor digiti qumti proprms brevis poliicis; e, M. extensor 



of man "I carpi radialis longus; /", M. 



'•'_ _ extensor carpi radialis brevis; 



Ol'igin (Fig. 81, «) from the lateral g, M. extensor carpi ulnaris; 



supracondyloid ridge of the humerus i'; ;rs".'r'ligle«T.he 



distad of the origin of the extensor ^'r'st- 



communis. 



The muscle passes along the ulnar border and dorsal surface 

 of the forearm between the extensor communis (Fig. 75, ;;/)and 

 the extensor carpi ulnaris (^?). Near the carpus it ends in a tendon 



