542 NAOKI SUGITA 



During the first week after birth, .when the increase of the 

 cortex in thickness is most energetic, cortical cell-lamination is 

 almost completed. Thus, at the fourth day after birth a light 

 band appears between the ]am. pyr. and the lam. gang., which 

 suggests that the differentiation of the latter is now at an end. 

 The ganglion cells are then in five or more rows. At birth, the 

 ental sublayer of the lam. mult, has seven or more rows of multi- 

 form cells, but these decrease with advancing age and by the 

 eighth day they have been reduced to four rows of cells or less. 

 I will reserve the details of these changes till I take up in a later 

 paper the development of each type of ganglion cell according to 

 age. 



According to His ('04) the transitional layers of the cerebral 

 cortex may be recognized in the human embryo at 4 months, 

 and, according to Melius ('12) they are still visible in the brain 

 of an eight months foetus and also of a newborn (stillborn) 

 child. Anyhow, the fact that they are not so distinctly visible 

 in a newborn human child as in a newborn rat, and that they 

 persist till after birth in the latter brain, shows, as already stated 

 by Donaldson ('08), that the albino rat is born with a brain 

 somewhat less mature than that of the human child. 



The transitional layers have not been subjected to measure- 

 ment, because they do not belong to the cerebral cortex proper, 

 and in making the measurements care has been taken to exclude 

 the transitional layers in the very young brains. 



VI. THE CELL-LAMINATION OF THE CORTEX OF THE ALBINO RAT 



In previous chapters (figs. 2, 4, and 6), I have described the lam- 

 inar structure of the cortex of the albino rat, as far as the cortex is 

 presented to view in my sections. A description of the cortical 

 lamination of the entire hemisphere is not included in the plan of 

 this study, but, as there has been no description previously pub- 

 lished on the cortical lamination of the albino rat, it has seemed 

 worth while to refer here to some papers on the cortical cell- 

 lamination in the Norway rat, from which the Albino has been 

 derived, and in some other mammals more or less closely related 

 and to compare the present observations with those previously 

 made. 



