MUSCLES ON THE BACK OF THE FOREARM. 367 



ulna, for some way downwards, and from a large share of the 

 interosseous ligament. It splits into four tendons, a little before 

 it passes under the ligamentum carpi annulare ; and these pass 

 through the slits in the tendons of the flexor sublimis. 



Inserted into the fore and upper part of the third or last bone 

 of all the four fingers. 



Use. To bend the last joint of the fingers. 



7. Flexor Longus Pollicis Manus, 



Arises, by an acute fleshy beginning, from the upper part of 

 the radius, immediately below its tubercle, and is continued down 

 for some space on the forepart of this bone. It has likewise 

 generally another origin from the internal condyle of the os 

 humeri, which forms a distinct fleshy slip, that terminates near 

 the upper part of the origin from the radius. 



Inserted into the last joint of the thumb, after having passed 

 its tendon under the ligament of the wrist. 



Use. To bend the last joint of the thumb.* 



8. Prenator Radii Qwdratiu, 



Arises, broad, tendinous, and fleshy from the lower and inner 

 part of the ulna ; the fibres run transversely, to be 



Inserted into the lower and anterior part of the radius, oppo- 

 site to its origin. 



Use. To turn the radius, together with the hand, inwards. 



Muscles of the External Side and Back of the Arm. 

 1 . Supinator Radii Longus, 



Arises, by an acute and fleshy origin, from the external ridge 

 of the os humeri, above the external condyle, nearly as far up as 

 the middle of that bone. 



* The thumb has but one flexor muscle on the front of the arm, although it 

 has three extensors on the back part. No animal but man has a distinct 

 flexor lengus pollicis muscle. In the monkey even, its place is supplied by a 

 branch of the communis digitorum tendons ; man only can bring the thumb in 

 direct opposition to the fingers, and make the hand a perfect instrument of 

 prehension. P. 



