GROWTH OF THE CEREBRAL CORTEX 25 
TABLE 7 
Showing the average corrected thickness of the cerebral cortex in the Norway rat for 
each brain weight group. 
FRONTAL 
SAGITTAL SECTION = HORIZONTAL SECTION GENERAL AVERAGE 
BRAIN WEIGHT eres 
GROUP 7S ee Ss 
bea Thickness | Thickness esa Thickness bias Thickness 
grams mm. mm. grams mm. grams mm. 
N XI 1.164 1.61 1.88 1.164 a teVe 1.164 1.79 
N XII 
N XIII 1.369 13 1.96 1.343 2.08 1.360 1.92 
N XIV 1.480 1.84 1.95 1.447 2.09 1.436 1.96 
N XV 1.537 1-82 2.04 1.520 2.24 1.532 2.03 
N XVI 1.629 1.88 2.08 1.663 2.19 1.640 2.05 
N XVII 1.739 1.94 2.07 1.747 2.19 1.742 2.05 
N XVIII 1.829 1.93 2.08 1.843 2.26 1.834 2.09 
N XIX 1.972 1.97 2.00 1.953 2.25 1.965 2.07 
N XX 2.052 1.87 1.96 2.018 2.08 2.041 1.97 
N XXxI 2.172 1.99 2.08 2.156 2.34 2.166 2.14 
N XXII 
N XXIII 2.345 1.86 2.345 2.22 2.345 2.04 
Within the limits of our material, the course of development 
of the cortical thickness in every locality seems, in general, simi- 
lar to that in the corresponding locality of the albino rat, the 
descriptions of which were given in the former paper (Sugita, 
17 a, pp. 574-577). 
VII. A COMPARISON OF THE NORWAY RAT WITH THE ALBINO RAT 
IN RESPECT OF CORTICAL THICKNESS 
The main object of the present paper is to compare the data 
from the Norway with those from the albino rat, in respect of 
the cortical thickness, a comparison of much interest, since the 
two forms are so closely related genetically and at the same time 
show differences in body size and in absolute brain weight which 
have been already noted. 
Comparing the mature brains, which weigh alike, of the both 
forms (table 8), the Norway cortex, whose thickness on the av- 
erage in Groups N XVI to N XX (brain weight average 1.844 
grams) is 2.05 mm., surpasses by 0.15 mm. or 8 per cent the albino 
cortex, whose thickness on the average in Groups XVI to XX 
