GROWTH OF THE CEREBRAL CORTEX ^43 



The first author to study the cell-lamination of the cerebral 

 cortex of the rodents was Bevan Lewis ('81). He took the rab- 

 bit and the Norway rat together as the representatives of the 

 rodents, but gave the details for the rabbit brain only, recording 

 for it the thickness of the cortex and of size of the cortical cells. 

 Bevan Lewis found cell-lamination in the cortex of the rabbit 

 similar to that in the rat, so I will here cite his types of the cell- 

 lamination for the rabbit only. 



He divided the entire cortex of the hemisphere into eight areas 

 distinguished by the laminar structure. 



1. Type of upper limbic arc. 



2. Modified upper limbic type. 

 .3. Outer olfactory type. 



4. Inner olfactory type. \ Comprised within the limits of the lower and 



5. Modified olfactory type./ anterior limbic arcs. 



6. Extra-limbic type. 



7. Type of cornu Ammonis. 



8. Type of olfactory bulb. 



Figure 10 reproduces the figures given by Lewis to show the 

 distribution of these types of cortical structure. So far as these 

 areas occur in my sections, a comparison of the lamination of 

 the cortex of the albino rat with that of the rabbit shows the two 

 cortices to be similar. It, however, seems hardly necessary to 

 record the details of the comparison on this occasion, although 

 such a detailed comparison has been made by me. According to 

 Lewis the parietal cortex of the rabbit has a thickness of 2.8 

 mm.' while at the corresponding locality (Locality VII shown in 

 figure 4) the cortex of the rat brain is 2.2 mm. thick (corrected 

 value) . From this, it would appear that the rabbit has a thicker 

 cortex, but systematic investigations would be required to really 

 determine this point. 



Recently Fortuyn ('14) has studied thoroughly the laminar 

 structure of the cortex in several rodents. He examined nine 



1 Measured on the section which was cut by the freezing microtome from the 

 fresh material and then hardened by osmic acid, stained by aniline black and 

 mounted in Canada balsam. According to his statement, we obtain, by this 

 method, the natural depth of the cortex, no shrinking occurring if the prepara- 

 tions have been carefully made (Lewis, '78). 



