62 NAOKI SUGITA 
albino rats, sexes combined, which was used in the present study, 
is identical with that listed in table 1 of the former paper (Sugita, 
"17 a), to which the reference should be made for this study 
also. 
These studies were made during the winter semester of 1916- 
1917. 
II. MEASUREMENTS AND ENUMERATIONS 
A. Area of the cortex in the sagittal section 
As previously described (Sugita, ’17 a), the sagittal section 
(fig. 1) was taken in a plane passing through the frontal pole 
and parallel to the mesial surface of the hemisphere. This 
section from each individual brain was projected on a sheet of 
paper by the Leitz-Edinger Projection apparatus, at a magnifi- 
cation of exactly twenty diameters, and the outline of the image 
then accurately traced on the sheet. At the transitional part 
of the cortex at the frontal pole to the olfactory bulb and at the 
subiculum, where the cortex goes over into the structure of the 
cornu Ammonis, the borderlines were drawn along the radiation 
of the cells in those parts (fig. 1). The anterior borderline 
(a-a’) is formed by a prolongation of the line bounding the dorsal 
surface of the olfactory bulb. The posterior borderline (p—p’) 
is ¢learly located, because this was drawn at the point where 
the thickness of the ganglionic layer abruptly diminishes at the 
beginning of the ganglion cell band characteristic for the cornu 
Ammonis. The area of the cortex, including the lamina zonalis, 
which contains no proper nerve cells, was then repeatedly 
measured to a square millimeter on the drawing, using the Ott 
Compensating Planimeter. The values obtained were then 
averaged, and 1/400 of the value, which corresponds to the 
cortical area on the slide, was recorded. This value was then 
converted into that for the fresh condition of the material, by 
the following procedure. 
On the outline, which was taken from the section on the slide, 
the diameter from frontal pole to the occipital pole (LZ. F) was 
measured and reduced, and, according to the formula given in 
the former paper (Sugita, 717 a), which reads 
