MUSCLES ON THE BACK OF THE FOREARM. 369 



and in its progress, fleshy, from the middle of ihe ulna, where 

 it passes over the ulna. Its round tendon is enclosed by a 

 membranous sheath, in a groove which is situated at the ex- 

 tremity of the ulna. 



Inserted, by its round tendon, into the posterior and upper 

 part of the metacarpal bone that sustains the little finger. 



Use. To assist the former in extending the hand. 



f 

 )g, froi 



5. Extensor Digitorum Communis, 



Arises, by an acute, tendinous, and fleshy beginning, from 

 the external condyle of the os humeri, where it adheres to the 

 supinator radii brevis. Before it passes under the ligamentum 

 carpi annulare externum, it splits into four tendons ; some of 

 which may be divided into several smaller ; and about the fore- 

 part of the metacarpal bones they remit tendinous filaments to 

 each other. 



Inserted into the posterior part of all the bones of the four 

 fingers, by a tendinous expansion. 



Vse. To extend all the joints of the fingers. 



6. Supinator Radii Brevis, 



Arises, tendinous, from the external condyle of the os humeri ; 

 tendinous and fleshy, from the external and upper part of the 

 ulna, and adheres firmly to the ligament that joins these two 

 bones. 



Inserted, into the head, neck, and tubercle of the radius, near 

 the insertion of the biceps, and into the ridge running from that 

 downwards and outwards. 



Use. To roll the radius outwards, and so bring the hand 

 supine. 



7. Indicator, 



Arises, by an acute fleshy beginning, from the middle of the 

 posterior part of the ulna ; its tendon passes under the same 

 ligament with the extensor digitorum communis, with part of 

 which it is 



Inserted into the posterior part of the fore-finger. 



Use. To extend the fore-finger separately. 



