178 THE MUSCLES 
five millimeters of the articular face of the 
head. 
Relations.—Outer surface with the ex- 
tensor carpi radialis brevis, extensor com- 
munis digitorum (Fig. 75, #), and extensor 
lateralis digitorum (Fig. 75, 2). Radial 
border with the pronator teres (Fig. 77, @). 
Inner surface with-the radius. 
Action.—Supinator of the hand. 
M. extensor brevis pollicis or extensor 
ossis metacarpi pollicis (Fig. 85, a) (includes 
M. abductor longus pollicis of man). 
Origin (Fig. 86, 2) by fleshy fibres from 
the ventral half of the lateral surface of the 
shaft of the ulna from the semilunar notch to 
the styloid process; from the ulnar half of 
the dorsal surface of the radius from the 
bicipital tubercle to a short distance distad 
of the middle of the bone; and from the 
interosseous membrane between these two 
areas. The fibres converge to form a strong, 
flat tendon (Fig. 84, @) which passes obliquely 
over the tendons of the extensor carpi radialis 
longus (¢) and brevis (/) to its 
oR EXTENSOR SUR- hone of the wrist is imbedded in the tendon 
FACE OF RADIUS AND 
ULNA, WITH THE at its insertion. 
AREAS OF ATTACH- . “ 
MENT OF MUSCLES. Relations. —Outer surface with the ex- 
a, long portion of tensor carpi radialis brevis, the extensor 
caput mediale of M. fe diate Fi t 
triceps: 4, caput lon- Communis digitorum (Fig. 75, m), extensor 
gum of M. triceps; ¢ Jateralis digitorum (Fig. 75, ), and extensor 
caput laterale of M. tri- , dicis. (Fie. 8 I f: ith th 
ceps; d, M. anconeus; 1NCICIS ( 1g. 5> c). nner surtace wl € 
¢, M, extensor carpi radius and ulna, and distad with the tendons 
ulnaris; 7, M. extensor 
indicis; aot supina- of the two extensores carpi radiales (Fig. 
tor; 2% . extensor 
brevis pollicis; i, M. 84, ¢ and /). . 
pronator teres; 7, M. Action.—Extends and abducts the pol- 
flexor profundus digi- 1 
torum; 4, M. biceps. /€X- 
