274 NAOKI SUGITA 
(found in the gyrus centralis anterior) is reported differently by 
different authors. The mean value is about 75 micra in average 
diameter. 
9. The size of the cortical cells, especially the Betz motor 
ganglion cells, of adult animals has no clear relationship to 
brain size or body size. These cells are notably large in the 
Felidae. 
10. As a general conclusion to this series of studies the follow- 
ing statement may be made: 
The morphological organization of the cerebral cortex is gener- 
ally precocious. The size of individual cortical nerve cells, the 
total number of cortical cells, and the thickness of the cortex, 
all attain nearly their full values at the same time and very 
early in life (corresponding to the weaning time in some rodents), 
after which the maturation of internal structures of the cell body 
and the nucleus continues. The brain weight and the cortical 
volume continue to increase even after this stage throughout the 
postnatal life, though not so rapidly as during the early period. 
This later growth is due principally to the development of the 
cell attachments, intercellular tissues (neuroglia tissue and blood- 
vessels), the ingrowth of axons into the cortex and their mye- 
lination, which together separate the cells from each other, and 
cause an increase in cortical volume. The cortical volume is 
primarily dependent on the size of individual cortical cells and 
their total number and it appears in animals belonging to a 
given zoological order to have a definite relationship to the 
size (or area of surface) of the body of the animal. 
