GROWTH OF THE CEREBRAL CORTEX 527 



in size to the cells of the lam. pyr., but slightly less stained. 

 The narrower (ental) sublayer which lies under the band poor in 

 cells forms the boundary to the white substance, and consists of 

 polymorphous cells, somewhat larger in size than the small pyra- 

 mids and tinted a little more deeply. In the area AA'-BB' , the 

 lam. mult, is the thickest layer and it occupies more than one- 

 third of the total thickness of the cortex. The lam. gang, is the 

 next in thickness, almost equal to the sum of the thickness of the 

 laminae pyr. et gran. int. The lam. gran. int. is the thinnest. 



The small area between BB' and CC has almost the same cell 

 lamination as the area AA'-BB' , but the cortex of this area be- 

 comes thinner towards the occipital pole. Especially the lam. 

 gang, loses in thickness remarkably. The characteristic of this 

 area is the appearance in the lam. gang, of the giant pyramids, 

 representing the largest nerve cells in the cerebral cortex of the 

 rat. 



The area CC'-DD', — DD' marking the occipital pole of the 

 cortex — covers as a cap the cornu Ammonis. In it, the total 

 thickness of the cerebral cortex diminishes on the average to a 

 half of that in the area AA'-BB'. In this area, the lam. pyr. 

 and the lam. gran. int. do not show much difference as compared 

 with the foregoing areas, the cells of the both layers staining 

 deeply. The lam. gang., however, becomes very narrow in this 

 area, and, in addition to this, the size of pyramids is much re- 

 duced. The lam. mult, loses greatly in thickness, but the char- 

 acter of the cells remains unchanged. Near the occipital pole 

 {DD') the light band which divides the lam. mult, into two sub- 

 layers disappears. 



The area DD'-EE' shows a quite characteristic cell-lamina- 

 tion, for example, the lam. zon. thickens distinctly while the 

 laminae pyr. et. gran. int. thicken suddenly at the part, where 

 the cortex is turned over the occipital pole and the surface of 

 the hemisphere makes contact with the dorsal surface of the 

 corpora quadrigemina. Immediately beneath the lam. gran, 

 int. comes the lam. mult., the lam. gang, almost vanishing for a 

 while. The lam. mult, exhibits, in this area, one layer instead 

 of two. 



