534 NAOKI SUGITA 



shift of the occipital end of the plane of section. The technique 

 used in obtaining the horizontal sections was similar to that em- 

 ployed for the sagittal and frontal sections. 



Figure 6 gives a schematic view of a horizontal section in this 

 plane, from the albino rat at about thirty days of age. It shows 

 diagrammatically the cell structure of the cortex and the posi- 

 tions of the localities subjected to measurement. The cortex of 

 the horizontal section is divided into areas as follows. 



The small area median to PP' , lying at the bottom of the 

 sagittal fissure between the two hemispheres, corresponds to the 

 similar area median to GG' in the frontal section (fig. 4), which 

 consists only of the cells- belonging to the lam. mult, (indus- 

 ium). As we pass towards QQ' , in the area PP'~QQ' , all the 

 cortical layers appear and increase in thickness. The area Q^}'- 

 RR' contains the knee of the frontal cortex and the line IX-IX' 

 runs through the very tip of the frontal pole. 



The area RR'-SS' is similar in cell-lamination to the area 

 AA'-BB' in the sagittal section (fig. 2) and the area KK'-LU 

 (fig. 4), and needs no explanation. At RR' the two sublayers of 

 the lam. mult, as seen towards SS' , fuse into one. 



In the area SS'-TT', as in the area LL'-MM' (fig. 4), the lam. 

 grar. int. increases markedly in thickness and cell-density, the 

 lam. gang, at the same time becoming thinner. 



In the area TT'-UV , the total thickness of the cortex de- 

 creases. Every layer takes part in this thinning and the cell 

 arrangement in every layer loses little by little its regularity. 

 Speaking broadly, the area TT'-UU' has a structure different 

 from that of SS'-TT', in that the lam. gran. int. becomes so 

 thin that it is difficult to recognize it, even in material fixed in 

 formol. Though the lam. mult, in this area does not sho w the 

 pale band separating it into two sublayers, yet we can distin- 

 guish the two sublayers, the ectal or subganglional sublayer 

 consisting of inflated cells and the ental, narrow band consisting 

 of several rows of the somewhat larger, polymorphous cells, 

 more deeply stained. 



The area UU'~WW' hasla modified structure. The fissura 



