THE MEDIAN NERVE 



'55 



It leaves the plexus by two roots. The fibres of the anterior root 

 come from the cervical roots of the plexus, and this root is described by 

 Chauveau as a separate nerve under the name of anterior brachial or 

 musculo-cutaneous. Leaving the plexus, the anterior root takes a course 

 which is almost vertically downwards. Crossing the direction of the 

 suprascapular artery, it meets the axillary artery, to the outer side 

 of which It is placed, immediately above the inner aspect of the 

 shoulder joint. It here winds round the inferior aspect of the artery 

 and joins the posterior root, thus forming a loop in which the axillary 

 artery rests. 



The fibres of the posterior root are derived from the eighth 

 cervical and dorsal contributions to the plexus. The nerve is 

 thus detached from the posterior division of the plexus. It then 

 descends to the posterior aspect of the axillary artery, crossing its 

 suprascapular branch. Uniting with the anterior root in the manner 

 described, the nerve takes an almost vertical course down the limb 

 in relation to the axillary artery, the direction of which it crosses, 

 being placed at first behind the artery and subsequently in front 

 of it. It then follows the course of the continuation of the axillary 

 artery, namely, the brachial, in front of which the nerve is placed. It 

 is frequently found behind the axillary throughout the extent of the 

 latter when it passes to the front of the vessel where the brachial artery 

 begins. 



It crosses the shaft of the humerus obliquely by following the course 

 of the artery just mentioned, passing to the inner side of the pre- 

 humeral artery and vein, which it crosses almost at right angles. In 

 front of the nerve is the coraco-humeralis muscle, to the inferior 

 tendon of insertion of which it is closely related. It then passes across 

 the artery to the biceps muscle, immediately behind the posterior 

 border of which muscle it now for a short distance runs. 



During its course the nerve may again cross the brachial artery to 

 its inner side, and place itself between the artery and the corresponding 



