GROWTH OF THE CEREBRAL CORTEX 205 
Since in the underfed the average cortical thickness in the 
sagittal and frontal sections was used in place of the standard 7’, 
based on the thickness of the sagittal, frontal and horizontal 
sections (compare Sugita, 717 a), therefore corresponding values 
of T have been used in calculating the standard values for the 
present comparison. 
For this comparison, the test animals may be considered in two 
groups, T.Il and T. II. In T. I groups, in which all test rats have 
a brain weight less than 1.0 gram, the average computed volume 
of the cortex is less than the standard by 16 per cent, while in 
T. II groups, which contain the test rats with brains weighing 
above 1.0 gram, it is more than the standard on the averagé by 1 
per cent. On the other hand, the cortical volume in C, I groups, 
which embraces the controls having brain weights less than 1.0 
gram, is on the average 2.4 per cent less, and in C. II groups, the 
controls with brain weights above 1.0 gram, it is on the average 
7.5 per cent more than the standard for the same age (table 11, 
last lines). As these comparisons are based on the numbers 
obtained by calculation and not on the direct measurement, slight 
discrepancies cannot be regarded as significant, and, as already 
noted, the results in the underfed are open to special correction of 
a few per cent for an accurate comparison. 
The underfed brains are much retarded in the weight develop- 
ment and the brains weighing up to 1.0 gram include those of 
ages up to sixteen days, at which age the normal rats have a brain 
weight 10 per cent heavier than the test rats (chapter V). We 
conclude, therefore, that, calculated by the formula L.F x W.D 
x T, the relative volumes of the cortex in the underfed are 
nearly the same as in the standard in the brains weighing more 
than 1.0 gram (T. II groups), while, on the contrary, they are 
considerably smaller than the standard in the case of the brains 
weighing under 1.0 gram or under the age of sixteen days, if the 
age be taken as the standard of comparison. 
It appears, therefore, that in rats underfed severely the cortical 
volume is considerably retarded in growth during the early period 
of development, but this is probably fairly compensated later 
when the brain attains a weight of more than 1.0 gram or an age 
