334 ABRAM T. KERR 



branch which suppHes the biceps muscle comes from a loop in 

 the first part of the median nerve. In another of the 155 cases 

 the lateral fasciculus does not divide as usual but the whole of 

 it forms the musculocutaneous nerve, the lateral head of the 

 median nerve being derived from the seventh cervical. In the 

 arm, the musculocutaneous nerve sends a branch to the median 

 nerve in this case (fig. 17). 



There are three plexuses, 1.71 per cent of the 175, in which 

 the musculocutaneous nerve arises from a trunk formed by the 

 union of the medial and lateral fasciculi of the plexus (fig. 27). 

 This trunk divides into median, ulnar and musculocutaneous 

 as previously noted in connection with these other nerves. There 

 are 9 instances, 5.14 per cent of the 175, in which the lateral 

 fasciculus of the plexus joins with the medial head of the median 

 and from the trunk thus formed the musculocutaneous nerve 

 arises as a single branch (if we ignore the branch to the coraco- 

 brachialis) in 6 (fig. 6), and in two or more branches in 3 cases. 

 In the above 12 plexuses the eighth cervical and the first thoracic 

 nerves may send fibers to the musculocutaneous nerve. 



In 9 of the above cases in which the musculocutaneous arises 

 from a stem common to it and to the median or median and ul- 

 nar, there are records for both sides of the body and in all of these 

 the arrangement on the other side was normal. Testut ('84) 

 found the musculocutaneous fused with the median in 6 instances 

 out of 105. 



There are 8 plexuses, 4.75 per cent of the 175, in which the 

 musculocutaneous nerve arises from the ventral division of the 

 cephalic trunk of the plexus (figs. 15 and 16). In these cases, 

 the seventh cervical nerve can take no part in the formation 

 of the musculocutaneous nerve unless the musculocutaneous 

 receives fibers of the seventh through its branches in the arm 

 from the median or some other nerve. My records are com- 

 plete through the arm for only 3 of these cases and these show no 

 branches from the median to the musculocutaneous nerve but 

 on the other hand in one of the plexuses there is a branch from 

 the musculocutaneous to the median nerve. 



My records for the musculocutaneous nerve are complete 



