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KENJI NITTONO 



head surface is l.():4.5(), whereas the mean ratio for the axis 

 cyhnders from all three branches is 1.0:9.25. 



These differences are possibly due to the fact, as Jackson and 

 Lowrey ('12) stated, that the head has already reached a rela- 

 tively large size at birth in comparison to the entire body, while 

 the axis cylinders are still immature, and thus the growth rate 

 of these two structures does not coincide. However, after this 

 period of rapid growth of the head area has passed, the ratios 



TABLE 14 

 Showing the relative areas of the heads and the relative areas of the axis cylinders in 

 fi- at different ages — albino rats — on increasing weight of head. The grouping of 

 the data in this table is similar to that in table 13, where the body iveights and ages 

 for the several groups are given. As the absolute measurements for the areas of 

 the axis cylinders are also given in table 13, they are omitted here, and the ratios 

 alone are presented 



for the enlargement, both of the areas of the head and the axis 

 cylinder, become more uniform, and in fact after the rat has 

 attained 16.6 grams in body weight (eighteen days of age) ap- 

 proximately similar relations are maintained as far as the obser- 

 vations go. In other words, from eighteen days after birth to 

 485 days a given area of the head surface is innervated by about 

 the same area of the axis cylinder, but before eighteen days the 

 areas of the fibers increase more rapidly than the area of the head. 



