84 



and use, 

 radius free 



and fixed. 



Extensor 

 carpi radialis 

 longior : 

 origin ; 



DISSECTION OF THE BACK OF THE FOREARM. 



the others, with its edges forwards 

 and backwards. Its anterior border 

 touches the biceps and the pro- 

 nator teres ; and the posterior is 

 in contact with both radial ex- 

 tensors of the wrist. Near its 

 insertion the supinator is covered 

 by two extensors of the thumb. 

 Beneath the muscle are the bra- 

 chialis anticus and the musculo- 

 spiral nerve, the extensors of the 

 wrist, the radial vessels and nerve, 

 and the radius. 



Action. The chief use of the 

 supinator longus is to bend the 

 elbow-joint; but if the radius is 

 either forcibly pronated or supi- 

 nated, the muscle can put the 

 hand into a state intermediate 

 between pronation and supination. 



If the radius is fixed, as in 

 climbing, the muscle will bring up 

 the humerus, bending the elbow. 



The EXTENSOR CARPI RADIALIS 



LONGIOR (B) arises from the lower 

 third of the external supracondylar 

 ridge of the humerus, from the 

 front of the external inter- 

 muscular septum, and from the 

 septum between it and the next 

 muscle. It lies 011 the short radial 

 extensor, being partly covered by 

 the supinator longus ; and its 

 tendon passes beneath the extensors 

 of the thumb, and the annular 



FIG. 35. SUPERFICIAL DISSECTION OF THE BACK OF THE 

 FOREARM. (ILLUSTRATIONS OF DISSECTIONS). 



Muscles : 



A. Supinator longus. 



B. Extensor carpi radialis longior. 

 c. Extensor carpi radialis brevior. 

 D. Extensor communisdigitoruin. 

 E . Extensor minimi digiti. 



F. Extensor carpi ulnaris. 

 Q. Anconeus. 



H. Extensor ossis metacarpi pol- 

 licis. 



I. Extensor brevis polhci.s. 

 j. Extensor longus pollicis. 

 K. Posterior annular ligament. 



L. Bands uniting the tendons of 

 the common extensor on the back of 

 the hand. 



N. Insertion of the common extensor 

 into the second and thii'd phalanges. 



Arteries : 



a. Posterior interosseous. 



1. Radial. 



2. Posterior carpal arch. 



b. Dorsal interosseous branch. 



4. Dorsal branches to thumb and 

 forefinger. 



