486 



M. J. GREENMAN 



TABLE 2 



1 Second and more distal count. 



Table 2 presents the results of the determinations of the 

 number of fibers in the right and left peroneal nerves of two 

 specimens of the Norway rat (Mus norvegicus) from which the 

 albino strain has been derived. 



Two counts were made, at different levels, in the case of the 

 right peroneal of no. 317; one count was made for each of the 

 other nerves. The average number of fibers in the right peroneal 

 nerves is 1992, in the left 2017 — a difference of 25 fibers or about 

 1.5 per cent. Since this difference is within the probable limits 

 of normal variation (2 per cent) we may conclude that the right 

 and left peroneal nerves contain approximately the same number 

 of fibers. 



These data on the Norway rat have been introduced here 

 merely to show the similarity of the number of medullated fibers 

 in the peroneal nerve on the two sides of the same animal. The 

 difference in the absolute number of medullated fibers in this nerve 

 in the Norway rat and in the albino calls for a special study. 



Returning to table 1, we note that the average of the proximal 

 counts of the three nerves is 2288 and that the average of the 

 distal counts of the three nerves is 2323, showing an average 

 excess of 35 fibers in the distal end of the nerve or an increase 

 of about 1.5 per cent in 10 mm. of nerve. Taking the average 

 of the two extremes 2288 and 2323 we get 2306 as the estimated 

 number in the middle portion of the nerve. The average of the 

 observed numbers of the middle counts is 2276, a difference of 

 a little more than 1 per cent. We can, therefore, safely assume 

 that 2306, the estimated number of the middle count is approxi- 



