GROWTH OF THE CEREBRAL CORTEX 73 
surely represent a group distinct from the small pyramids, were 
counted alone. So, by subtraction, the number of small pyra- 
mids only in the lamina ganglionaris was obtained. In counting 
the ganglion cells, I adjusted the lower line on the net-microme- 
ter accurately on the border between the lamina ganglionaris and 
the lamina multiformis, because between the lamina ganglionaris 
and the lamina granularis interna there is found a pale band 
poor in cells and therefore it was not convenient to adjust the 
upper line of the net-micrometer at this border. The number 
of cells observed, in a slice of 0.1 mm.? in area and 10 micra 
thick on the slide,’ were in the similar manner recorded and 
by the use of the same correction-coefficients, as were used 
in the case of the pyramidal cells, were reduced to the number 
for the fresh condition of the brain. 
Out of the total number of cells, which came in view in the 
microscopic field, about one-third does not contain the nucleoli 
in the cell nuclei. This means that the nucleoli in question lie 
outside of the section. Nevertheless I counted the cells having 
nuclei without nucleoli together with those in which nucleoli 
were to be seen, because my object was to ascertain the cell 
density in the locality chosen and not to determine the total 
number of nerve cells in a series of sections. In the latter case, 
the double counting of one and the same cell must be necessarily 
avoided. On the other hand, the cells which were represented 
in the section by only fractions of the cell bodies without nuclei 
were omitted from the counting. The number of such cells 
was small. Neuroglia nuclei, which were to be easily distin- 
guished by their smaller size, and the intima cells of the capil- 
laries, if they came in view, were not counted. 
Table 3 shows the results of these enumerations. 
III. DISCUSSION 
D, The area of the cortex in the sagittal section 
Examining table 1 and chart 1 (graph s), which give the area 
of the cortex in the sagittal sections of the albino rat brain, it is 
seen that the area increases steadily with increasing brain weight. 
