250 



KENJI NITTONO 



first column shows the areas of the enth-e cross-section of the 

 fibers, the second column gives the areas for the axis cylinder, 

 while the third column gives the per cent of the total area repre- 

 sented by the axis cylinder. The very last column in the table 

 gives the average of the four values for the percentage area of 

 the axis at each body weight. As these last averages show, the 

 area of the axis is about 44 per cent in the smallest rats 

 examined, but after puberty it rises to about 50 per cent. 



TABLE 1.3 



Shoiring the areas of the fibers and of the axis cylinders in ix- in the three branches 

 and in the fifth nerve at different ages — albino rat 



The vertical averages from the data in table 13 are: 



First branch 44 per cent 



Second branch 47 per cent 



Third branch 48 per cent 



Fifth nerve root 50 per cent 



Range 



40 to 48 per cent 

 42 to 55 per cent 

 44 to 50 per cent 

 46 to 55 per cent 



This tabulation suggests that there are local differences in 

 this character, as the average values for the areas increase from 

 the first branch to the trunk and their respective averages corre- 

 spond in general to the range in the values observed. 



The present results agree very well with the previous deter- 

 minations for the area of the axis as reported by Donaldson ('00) 



