330 ABRAM T. KERR 



tribute to the formation of the median in the axilla but forms a 

 large nerve which, after giving off three branches to the coraco- 

 brachialis muscle, divides into two branches. These pierce the 

 coracobrachialis muscle separately, one becomes the musculo- 

 cutaneous and the other joins the median nerve about the middle 

 of the arm (fig. 17). The median nerve beyond this point may 

 contain fibers from all the spinal nerves which contribute ordi- 

 narily to its formation. The lateral head of the ulnar in this case 

 arises from the lateral head of the median (seventh cervical) and 

 sends branches to the medial head of the median as well as to the 

 ulnar nerve. 



In 3 of the remaining 14 plexuses, the medial and' lateral 

 fasciculi of the plexus join to form a common stem that immedi- 

 ately splits up into median, ulnar and musculocutaneous nerves 

 (fig. 27). 



In two instances, the ulnar and median nerves arise from a 

 common stem formed by the union of the lateral head of the 

 median with the medial fasciculus of the plexus. Almost im- 

 mediately after this stem is formed it divides into median and 

 ulnar nerves (fig. 28). The above five cases have already been 

 noted in discussing the ulnar nerve. 



In 9 cases, the musculocutaneous nerve does not separate 

 from the lateral fasciculus of the plexus, but the lateral fasciculus 

 of the plexus joins the medial head of the median nerve to form 

 a common stem. This passes down the arm and gives off the 

 musculocutaneous nerve as a single definite nerve in 6 instances 

 (fig. 6), but as a number of separate branches in 3 instances. 



There were a number of other instances in which there were 

 interesting interrelations between the median and the musculo- 

 cutaneous nerves. Some of these will be considered in the 

 description of the musculocutaneous nerve. 



Of the 152 plexuses in which the median nerve arises by two 

 heads in the usual way, 72, or 47.36 per cent neither receive nor 

 give off any branches (figs. 5 and 7). But in the remaining 

 cases one or the other of the heads of the median nerve either 

 receive or give off branches. 



The medial head of the median receives an additional branch 



