UPPER EXTREMITY AND THORAX, ANTERIOR. 293 



DISSECTION. 



Trace the radial nerve to the posterior margin of the tendon of the supinator 

 longus (brachioradialis). The radial artery until it disappears under the 

 extensor tendons of the forearm, and its branches in the forearm. The 

 ulnar artery to the wrist, and its branches. 



The Radial Nerve. Fig. 66. 



The anterior branch of the musculospiral nerve. It 

 descends behind the inner portion of the supinator longus 

 muscle, until at the lower part of the muscle it passes 

 backward to the posterior surface of the thumb and hand. 



The Posterior Interosseous Nerve. 



This is the posterior branch of the musculospiral nerve 

 and disappears from the front of the elbow by passing into 

 the substance of the supinator brevis muscle. 



The Radial Artery. Figs. 66, 67. 



This is the outer branch of bifurcation of the brachial, 

 the direction of which it continues. The portion of the 

 artery that lies in the forearm extends from below the 

 elbow to the wrist, where the artery passes posteriorly 

 under the extensor tendons of the thumb. 



Its course is outward and downward, between the prona- 

 tor radii teres and the supinator longus (brachioradialis) 

 (the latter of which overlaps the artery in front), then 

 between the tendons of the flexor carpi radialis and the 

 supinator longus. The artery is indicated by a line drawn 

 from just below the centre of the elbow to the inner side 

 of the styloid process of the radius. The radial nerve is 

 at the radial side of the artery for the upper two-thirds of 

 its course, but not in close relation with it, and is not seen 

 in ligation of the artery. 



The artery rests upon the tendon of the biceps, supinator 



