BRACHIAL PLEXUS OF NERVES IN MAN 321 



metrical because different types of plexus are found on the two 

 sides but both types are in the same group. Six are in group 1 

 and 1 in group 2. Of those in group 1, in 4 type A is on one side 

 and type B on the other. In 2 of these type A is on the right and 

 in 2 it is on the left. In two bodies type B is found on the right, 

 type C upon the left. In the case where both plexuses are in 

 group 2, type E is on the right and type F on the left. 



THE ORIGIN OF THE BRANCHES FROM THE BRACHIAL PLEXUS 



As will be seen from figures 1 to 8 some of the branches of the 

 plexus arise from the rami of the spinal nerves forming the 

 plexus, some from the cephalic and caudal trunks and some from 

 the medial, lateral, and posterior fasciculi. In my study of the 

 nerves of the plexus, the trunks and fasciculi were not broken 

 up and subdivided so that one could see just which spinal nerve 

 contributed to each branch, and as demonstrated by my macera- 

 tion experiments, this is impossible in a great many cases even by 

 this method, let alone by dissection. It is assumed then that 

 if a nerve arises from a trunk formed by branches from two or 

 more spinal nerves that both or all of them may send fibers to 

 the nerve. It is recognized, of course, that in some cases only 

 one of the nerves may contribute to a branch, but there is no 

 way of determining by anatomical methods when this occurs or 

 which nerve it is. It seems best, therefore, to consider all of the 

 nerves that help to form a trunk or fasciculus as potential ele- 

 ments in each branch from the trunk or fasciculus. 



In the usual descriptions, the lateral fasciculus is said to termi- 

 nate by dividing into the musculocutaneous nerve and the lateral 

 head of the median nerve; the medial fasciculus by dividing into 

 the ulnar nerve and the medial head of the median nerve; the 

 posterior fasciculus by dividing into the axillary and radial 

 nerves. It has already been shown that this does not always 

 occur but I shall not deal separately with the percentage occur- 

 rence of this division of each of these fasciculi into medial and 

 lateral branches but shall consider it in connection with each 

 of the branches. 



