GROWTH OF THE CEREBRAL CORTEX 161 
in size, but the internal structure matures progressively as the 
brain weight increases. The cell body and the nucleus of the 
ganglion cells increases in size continuously throughout life. 
The last entry for the nucleus of the ganglion cells is an exception 
to this statement. 
3. As compared with the corresponding cells in the albino rat, 
the pyramids in the adult Norway rat (Groups N XIII to N XX) 
exceed those in the Albino in diameter on the average by 4 per 
cent and in volume by 12 per cent and the ganglion cells also 
exceed in diameter on the average by 7 per cent and in volume 
by 20 or more per cent. 
4. The course of development and the morphological changes 
in the Norway cells are similar to those in the albino rat, if com- 
pared at like ages. At the same age, the Norway brain weight, 
less 18 per cent, is taken as equal to the brain weight of the 
Albino. 
