MUSCLES OF THE THORACIC LIMBS. 



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 (n). 

 Inner surface with the supinator (Fig. 

 85, b~] and the extensor pollicis brevis 



(Fig. 85, a). 



. . ... FIG. 84. ARRANGEMENT OF 



Action. Extensor of the four ulnar THE TENDONS ON THE 



rjjo-jts BACK OF THE HAND. 



.., , . ., ,. a, M. extensor communis 



M. extensor dlgltOrum laterallS digitorum; J,M. extensor late- 



(Fig. 75, n\ (This corresponds in posi- ralis digitorum; f , M. exten- 



. sor mdicis; a, M. extensor 



tion to the extensor dlgltl quintl proprius brevis pollicis; e, M. extensor 

 of man ^ carpi radialis longus; _/", M. 



extensor carpi radialis brevis; 

 Origin (Fig. Si, n) from the lateral g, M. extensor carpi ulnaris; 



supracondyloid ridge of the humerus SS^^ffft 



distad of the origin of the extensor wrist - 



communis. 



The muscle passes along the ulnar border and dorsal surface 

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

 the extensor carpi ulnaris (0) . Near the carpus it ends in a tendon 



