GROIAT^H OF THE CEREBRAL CORTEX 



525 



into several areas characterized by the difference of cell- 

 lamination. 



The cerebral cortex of the albino rat has five cell layers (fig. 

 3) if a typical locality be taken. The most external layer is 

 the lamina zonalis (I), which has a few scattered glia-cells. 

 Under this, there is the lamina pyramidalis (III) consisting of 

 typical, deeply-staining, pyramidal cells lying closeh^ together, 



Fig. 2 Diagram of the sagittal section, from the albino rat brain weighing 1.5 

 grams, at about 30 days in age, showing the cell-lamination of the cortex and 

 the localities at which the thickness of the cortex was measured. //' is the level 

 from which the frontal section was to be taken. Lines AA', BB', CC, DD', EE' 

 and FF' indicate the borders of the areas showing different types of cell-lamina- 

 tion. 



which corresponds to the third layer of Brodmann ('09). In 

 the rodent brain, the lamina granulans externa (II), or the sec- 

 ond layer of Brodmann, is always indistinct, and it is almost 

 impossible to distinguish it from the lam. pyr. (III). Beneath 

 the lam. pyr., the lamina granular is interna (IV) is situated, com- 

 posed of crowded, deeply-staining, small granules, somewhat 

 resembling glia-cells. Below this laj^er, there is the lamina gan- 

 glionaris (V), which has dispersed, large-sized, deeply-staining 



