BRACHIAL PLEXUS OF NERVES IN MAN 299 



upon the position of the plexus along the body axis. Those 

 plexuses that receive branches from the fourth cervical nerve 

 would be more cephalic than those that do not. The terms 

 have been used by some, especially prefixed or postfixed, to indi- 

 cate the position of the supposed greatest strength of the plexus, 

 that is, the position of the largest nerves. 



The plexuses of group 1, in which a branch from the fourth 

 cervical nerve joins the plexus may be classified as cephalic, those 

 of group 3 in which the fifth cervical nerve sends a branch to the 

 cervical plexus as caudal, while those of group 2 in which the 

 fifth neither receives nor gives off a branch as intermediate. 



Between the most cephalic plexuses of group 1, with the largest 

 sized branch from the fourth cervical nerve and the most caudal 

 plexuses of group 3, with the largest branch from the fifth to the 

 fourth, there is a variation of almost one spinal nerve. This 

 may be accounted for either by a shifting of the plexus along the 

 spinal cord in either a cephalic or a caudal direction without 

 change in its relative size or the number of elements entering it, 

 or by an increase or decrease in the number of nerve fibers enter- 

 ing the plexus. 



If it is a shifting of the plexus that takes place, then when the 

 branch of the fourth cervical nerve is large the branch from the 

 second thoracic should be wanting, and when the fifth sends a 

 branch to the fourth there should be a large branch from the 

 second thoracic nerve to the plexus. 



If it is an increase or decrease in the number of nerve fibers 

 that enter the plexus that occurs, then the expansion or contrac- 

 tion of the plexus may take place on its cephalic or caudal side 

 or both. 



From my own observations just given it is obvious that there 

 is a variation in the cephalic limits of the plexus but unfortunately 

 I have been able to study the caudal limits in only a few of these 

 plexuses. Moreover, I have been able nowhere to find records 

 of cases which show that when the fourth cervical nerve does not 

 enter the plexus the second thoracic invariably does, and in- 

 versel}", whether when -the fourth cervical nerve enters into the 

 formation of the plexus the second thoracic does not, or as to 



