GROWTH OF THE CEREBRAL CORTEX 123 
but in several stages of growth, a few were measured, in order 
to be able to make some comparisons. 
The study of the cells under the microscope was made with a 
Zeiss Comp. Ocular no. 6 with a micrometer, combined with the 
objective 2 mm., oil immersion. Each division in the micrometer 
scale was equal to two micra. The measurement of the cell 
size was executed in the following way: the transverse diameter 
of the cell body (the greatest width of the cell body) was meas- 
ured on a line, parallel to the base line, which crossed about the 
middle of the nucleus. For the longitudinal diameter the meas- 
urement Was made vertical to the transverse diameter from the 
base of the cell body to the beginning of the apical dendrite. 
This last limit was assumed to be at the point where the Nissl 
bodies are no more to be seen and the side lines of the apical 
dendrite begin to run nearly parallel to each other. Sometimes 
this upper limit was very hard to determine, especially in fully 
grown cells, because of the irregularity of the cell outline and 
the relatively slow transition from cell body to the apical den- 
drite. In these latter cases, the upper limit Was somewhat arbi- 
trarily fixed, but this procedure has apparently been without 
much effect on the results. 
The measurements of the ten largest cells of the same kind 
from within the fixed locality in the same individual were then 
averaged for each diameter and recorded on cards without any 
correction. The average measurements from the frontal section 
and the horizontal section are denoted in the records by the 
letters F and H, respectively. The individual averages for each 
series of ten cells in each section have all been tabulated and 
the respective averages for the brain-weight groupsfound. The 
values for the individuals in each brain-weight group are so 
well correlated with their respective individual brain weights 
that it has seemed necessary to publish only the averages for the 
successive brain-weight groups. Table 1 contains the cell 
measurements on the frontal section averaged for each brain- 
weight group. The results of the measurements on the hori- 
zontal sections, Which were taken from the other individuals, 
