720 



MUSCLES OF THE FOREARM. 



Extensor ossis metacarpi pollicis manus, (Fig. 230.) 

 This muscle, called also extensor primi pollicis, arises fleshy 

 from the posterior part of the ulna, just below the anconeus 

 from the interosseous ligament, and from the posterior part 

 FIG. 230. of the radius, below the supinator brevis. 

 It ends in a round tendon which goes 

 over the radial extensors, and through a 

 groove on the styloid side of the radius, 

 to be inserted into the os-trapezium and 

 into the base of the metacarpal bone of 

 the thumb. A bursa is seen where the 

 tendon passes through the groove of the 

 radius. Function. To extend the meta- 

 carpal bone of the thumb. 



The extensor minor, or secundi pollicis, 

 (Fig. 230,) arises, tendinous and fleshy, 

 from the posterior part of the ulna, below 

 its middle, and from the interosseous 

 ligament and radius. It descends and 

 passes through the same groove of the 

 radius with the last muscle, and is in- 

 serted into the posterior part of the first 

 phalanx of the thumb. Function. To 

 extend the first phalanx of the thumb. 



The extensor major, or tertii pollicis, 

 (Fig. 230,) arises, above the middle of 

 the ulna on its posterior part, from the interosseous liga- 

 ment, and from the back of the radius. It ends in a tendon 

 which passes through a separate groove of the radius, and 

 goes to be inserted into the last phalanx of the thumb. A 

 synovial membrane supplies its tendon at the wrist. 

 Function. To extend the last phalanx of the thumb. 

 The indicator (Fig. 230) arises tendinous and fleshy from 



FIG. 230 represents the Deep Muscles on the back of the Forearm, a Inferior 

 portion of the humerus. 6Olecranon process, c Body of the ulna, d Anco- 

 neus. e Supinator radii brevis. / Extensor ossis metacarpi pollicis. g Exten- 

 sor minor pollicia. h Extensor major pollicis. i Indicator, j First dorsal 

 interossei. 



