GEOWTH OF THE CEEEBRAL CORTEX 535 



rhinalis, denoted by V, lies midway in this area. Between the 

 fissura rhinalis and the cornu Ammonis, there is a light band 

 free from cells in the place of the lam. gran, int., although, near 

 the fissura rhinalis, this layer has a small number of more or less 

 scattered cells. The lam. pyr. shows distinctly two sublayers, 

 the ectal or subzonal one consisting of a band of the large- 

 sized, deeply-stained, crowded pyramids, and the other ental 

 sublayer of a band of somewhat lightly stained, smaller-sized, 

 inflated cells, which are less crowded than in the subzonal sub- 

 layer. This ental sublayer occupies about two-thirds of the thick- 

 ness of the entire lam. pyr. The lam. gang, is scarcely to be 

 distinguished and the lam. mult, is here formed by a single 

 layer and is also thin. I would like to call attention here to the 

 fact that though the large-sized, deeply-stained pyramids lying 

 subzonally in the area UU'-WW are usually held to be derived 

 from the cells of the lam. pyr. by change of form, I am much in- 

 clined to attribute these cells to another source, but the discus- 

 sion of this question must be reserved for another paper. 



The area WW'-X' shows a cell-lamination, which is very 

 • peculiar in that the subzonal sublayer of the lam. pyr. suddenly 

 increases in thickness, the pyramids become crowded, and the 

 ental, epigranular sublayer becomes so thin as to be almost in- 

 distinguishable. The light cell-free band corresponding to the 

 lam. gran. int. widens here. 



At X' the lam. pyr. ceases abruptly. In the area X'-YY', 

 the cell-free parts of the cortex becomes much thickened, the 

 laminae pyr. et gran. int. disappear entirely and the remainder 

 of the lam. gang, undergoes a sudden thickening and becomes 

 characterized by large-sized pyramids well dispersed. The lam. 

 mult, also disappears at YY', giving place to the pyramids of the 

 lam. gang., which continues into the cell band of the cornu Am- 

 monis beyond YY'. The area X'-YY' is the same part of 

 the brain as that represented in the area EE'-FF' of figure 2, 

 namely the subiculum cornu Ammonis. 



Figure 6 shows also the positions of the five localities at which 

 the thickness of the cortex was measured on the horizontal 

 section. 



