THE MUSCLES 



FIG. 86. LATERAL 

 OR EXTENSOR SUR- 

 FACE OF RADIUS AND 

 ULNA. WITH THE 

 AREAS OF ATTACH- 

 MENT OF MUSCLES. 

 <z, long portion of 

 caput mediale of M. 

 triceps; b, caput Ion- 

 gum of M. triceps; c, 

 caput laterale of M. tri- 

 ceps; d, M. anconeus; 

 e, M. extensor carpi 

 ulnaris;/, M. extensor 

 indicis; g, M. supina- 

 tor; A, M. extensor 

 brevis pollicis; i, M. 

 pronator teres; /, M. 

 flexor profundus digi- 

 torum; k, M. biceps. 



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, ;/). Radial 

 border with the pronator teres (Fig. 77, q). 

 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, //) 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, d] which passes obliquely 

 over the tendons of the extensor carpi radialis 

 longus (e) and brevis (f) to its 



Insertion into the radial side of the base 

 of the first metacarpal. The radial sesamoid 

 bone of the wrist is imbedded in the tendon 

 at its insertion. 



Relations. Outer surface with the ex- 

 tensor carpi radialis brevis, the extensor 

 communis digitorum (Fig. 75, ;;/), extensor 

 lateralis digitorum (Fig. 75, n), and extensor 

 indicis (Fig. 85, c]. Inner surface with the 

 radius and ulna, and distad with the tendons 

 of the two extensores carpi radiales (Fig. 

 84, e and/). 



Action. Extends and abducts the pol- 

 lex. 



