GROWTH OF THE CEREBRAL CORTEX 2 
respectively. The only other large difference is 15 per cent at 
locality VI. 
Accordingly, in the mature rats, the average thicknesses in the 
sagittal, frontal and horizontal sections are respectively 6.7, 9.1 
o4|__+ 
| | 
| 
Q2;/—_+ —_ + —_J—_+_ —_+}_ __+ = = call = ++ 
| | | 
° 
(EA ba ea SE La elle i 
{DEA OSE Sd GMa TAO ETOMECOM dM een tai eas gee 
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Chart 3 Giving the average thickness of the cortex for each brain weight 
group at localities I, II, III, IV and V in the sagittal section and the average 
thickness at five localities in each brain weight group in sagittal section. Based 
on table 4. -— -—-— (above the heavy line) Cortical thickness at locality I. 
Corrected. ------- (above the heavy line) Cortical thickness at locality IT. 
Corrected. -— -— -— (near the heavy line) Cortical thickness at locality III. 
Corrected. --------- (below the heavy line) Cortical thickness at locality IV. 
Corrected. -—-—- — (below the heavy line) Cortical thickness at locality V. 
Corrected. ° 
weight group. 
°S Average thickness of the sagittal section by each brain 
and 8.0 per cent greater and the general average thickness is, 
consequently, 8 per cent greater in the Norway than in the al- 
bino rat, while the brain weights are almost the same (about 1.8 
grams). 
As regards the differences in cortical thickness here found a 
few comments may be made. Possibly all of the larger differ- 
