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NAOKI SUGITA 



phase, the cortex gains in thickness very slowly though continu- 

 ously throughout the first year of life, while the brain continues to 

 increase in weight according to age much more rapidly, so that, 

 in the full grown rat, whose body weight amounts to more than 

 200 grams, the cortical thickness attains on the average nearly 

 1.94 mm. The general average thickness of the groups XI to 

 XX is 1.88 mm. (table 9). 



TABLE 14 



Showing (column> B) brain weights, {column C) their ratios to the initial weight at 

 birth, {column D) the cube roots of the numbers given in column C, indicating 

 roughly the rate of increasing size, {column E) the average thickness of the cerebral 

 cortex corresponding to the given brain weights and {column F) their ratios to the 

 initial cortical thickness at birth, in every group 



Table 14, which is based on table 9, presents the relations 

 existing between the increase of the brain weight and the increase 

 of the cortical thickness. The figures in column B of table 14 

 show the average brain weights by groups. Columr C shows the 

 ratio of the brain weight of each group compared with the initial 

 brain weight at birth. Column D shows the cube roots of the 



