SHOULDER, ARM, FOREARM, HAND. POSTERIOR PART. 351 



dyle ; (2) the posterior surface of the ulna ; (3) posterior border of the ulna, in 

 common with the flexor carpi ulnaris. Dissection of this latter muscle requires 

 care. 



The deep group of muscles and their origin (Figs. 245 and 246) : 

 i. The extensor longus pollicis ulna and interosseous membrane. 



Supinator brevis 



Extensor oasis metacarpi pollicis 



Extensor brevis pollicis 

 Extensor longus pollicis 



Radial extensors 



Flexor carpi uliiaris 



Flexor profundus digitoru 



Extensor indicia 



Extensor oarpi ulnaria 



FIG. 245. THE DEEP LAYER OF THE BACK OF THE FOREARM. 



2. The extensor brevis pollicis radius and interosseous membrane. 



3. The extensor ossis metacarpi pollicis radius interosseous membrane and 

 ulna. 



4. The extensor indicis from the ulna. 



In view of the special importance of the three extensors of the thumb and the 



