302 ABRAM T. KERR 



From the above it is clear that the largest nerve to enter the 

 plexus is the seventh or eighth in 19 of the 27 cases or in over 70 

 per cent. (The seventh is largest in 7, the eighth in 6 and the 

 seventh and eighth equally large in 6.) 



When we attempt to correlate this with the division of the 

 plexuses into groups, we find that in group 1, in which the fourth 

 cervical nerve enters the plexus, the largest nerve and the point 

 of greatest strength is in the sixth cervical nerve in one case, the 

 seventh in 5 cases, the eighth in 5 cases and the seventh and 

 eighth equally in 7 cases. That is, while all 18 of the above plex- 

 uses would be classed as cephalic because of receiving a branch 

 from the fourth cervical nerve, those cases in which the largest 

 nerve is the eighth or seventh and eighth would most surely 

 be classed as postfixed and only those cases in which the largest 

 nerve is the sixth and possibly the seventh would be classed as 

 prefixed. That is, each group would have to be subdivided so 

 that the cephalic plexuses (my group 1) would be subdivided into 

 prefixed, postfixed and intermediate. 



The diameter of a nerve depends not only upon the number 

 of nerve fibers but also upon the amount of connective tissue, 

 the amount of fat and the quantity of moisture in it. In making 

 a dissection it is very difficult to tell when all the connective tissue 

 has been removed leaving only that tissue which we call epi- 

 neurium. There is no line of demarcation between the epineurium 

 and the surrounding connective tissue and different dissectors 

 are not liable to agree as to the dividing line. Furthermore in 

 my series it was impossible to tell if a student had removed the 

 same relative amount of connective tissue from the different 

 nerves. The septa that the epineurium sends through the nerve 

 separating and binding together the bundles of nerve fibers are 

 of greatly varying size and blend to some extent with the peri- 

 neurium that immediately surrounds the nerve bundles. 



In very lean persons there is little fat in the epineurium, but 

 in the fat, there is a very considerable amount, especially in the 

 septa between the nerve bundles. An indication of the amount 

 of variation may be seen in sections of a nerve from a fat and a 

 lean body respectively. 



