afterwards 

 superficial : 



Extensor 

 of first 

 phalanx : 



origin ; 



insertion 



and use. 



Extensor of 

 second 

 phalanx : 



DISSECTION OF BACK OF FOREARM. 



forearm between the last muscle 

 and the radial extensors of the 

 wrist (fig. 35). Opposite the 

 carpus the radial artery winds 

 backwards beneath its tendon. 

 Between the contiguous borders 

 of this muscle and the supinator 

 brevis the posterior interosseous 

 artery (a) appears. 



Action. By this muscle the 

 thumb is carried outwards and 

 backwards from the palm of the 

 hand, and the hand is moved to 

 the radial side. 



The EXTENSOR BREVIS POLLICIS 



(ext. primi internodii poll. ; F ; 

 fig. 35, 1.) is the smallest muscle of 

 the deep layer, and its tendon ac- 

 companies that of the preceding 

 extensor. Its origin, about one inch 

 in width, is from the radius and the 

 interosseous membrane, close below 

 the attachment of the last muscle 

 (fig. 36). The tendon passes through 

 the same space in the annular liga- 

 ment as the extensor of the meta- 

 carpal bone, and is inserted into 

 the base of the first phalanx of 

 the thumb. With respect to sur- 

 rounding parts, this muscle has 

 similar relations to the preceding. 

 Action. It extends first the 

 proximal phalanx and then the 

 metacarpal bone, like its com- 

 panion. 



The EXTENSOR LONGUS POLLICIS 



(ext. secundi internodii poll. ; G) 



FIG. 37. DEEP DISSECTION OF THE BACK OF THE FOREARM (ILLUSTRATIONS 

 OF DISSECTIONS). 



c. Ending of the anterior inter- 



MuscUs : 



A. Supinator longus. 



B. and c. Radial extensors of the 

 carpus, cut. 



D. Supinator brevis. 



E. Extensor ossis metacarpi pollicis. 



F. Extensor brevis pollicis. 



G. Extensor longus pollicis. 

 H. Extensor indicis. 



i. Posterior annular ligament. 

 Arteries : 



a. Posterior interosseous. 



b. Interosseous recurrent. 



osseous. 



d. Radial. 



e. Dorsal branches to the thumb 

 and forefinger. 



f. Dorsal carpal arch. 



g. Two dorsal interosseous of the 



hand. 



j\ cries : 



2. Radial. 



3. Posterior interosseous at its 

 origin, and 



4. Near its~ending on the back of 

 the carpus. 



