MUSCLES OF THE THORACIC 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, 2) of the triceps. 
Radial surface with the extensor longus 
(4) and extensor brevis. Ulnar surface 
with the extensor digitorum lateralis (7). 
Inner surface with the supinator (Fig. 
85, 4) and the extensor pollicis brevis 
(Fig. 85, a). Fic. 84.—ARRANGEMENT OF 
Action.—Extensor of the four ulnar tue TENpDons on THE 
BAcK OF THE HAND. 
digits. : 
os Z a, M. extensor communis 
M. extensor digitorum lateralis digitorum: 4, M. extensor late- 
: ‘a : i ;_ ralis digitorum; c, M. exten- 
(Fig. 755 7) (This corresponds ah ail sor indicis; d, M. extensor 
tion to the extensor digiti quinti proprius brevis pollicis; 2, M. extensor 
carpi radialis longus; 7, M. 
of man.) extensor carpi radialis brevis; 
Origin (Fig. 81, 2) from the lateral g, M. extensor carpi ulnaris; 
supracondyloid ridge of the humerus fi ee eee 
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, #) and 
the extensor carpiulnaris(0). Near the carpusit ends ina tendon 
