GROWTH OF THE CEREBRAL CORTEX 139 
the full size (10 days), but continues to grow steadily, though 
slightly, throughout later life. The size of the nucleolus in the 
ganglion cells is relatively much larger than in the pyramids. 
As for the developmental phases of the ganglion cells accord- 
ing to age, a statement similar to that made concerning the pyra- 
mids of the lamina pyramidalis holds true, though in the ganglion 
cells the size development seems to be accomplished in general 
somewhat earlier. In a brain under 1.2 grams in weight, more 
mature ganglion cells are seen mixed up with those less mature, 
indicating that the development of the ganglion cells is not uni- 
form, but that some progress more slowly. In a brain weigh- 
ing more than 1.3 grams, all the ganglion cells seem to have 
already passed the first phase of development in size, and all the 
cells are now of full size and probably fully functional. 
One observation which I think it important to notice here is 
that cells in the same layer but in different parts of the cortex 
do not always show a like degree of development at a given age. 
Some cells or some cell groups are more precocious or more re- 
tarded than their neighbors. My observations apply only to the 
size and morphology of the most developed cells found together 
in a selected locality, regardless of the relative maturity of that 
locality. So the statement that the ganglion cells attain full 
size at ten days does not necessarily mean that the lamina gang- 
lionaris is completely mature at that age, but it only applies to 
the size or morphology of the most advanced cells found in the 
layer. As a matter of fact, the lamina ganglionaris matures in 
toto earliest, so that in a brain weighing 1.3 grams all the gang- 
lion cells found in the lamina ganglionaris are apparently com- 
pletely mature, while at the same age the lamina pyramidalis 
still contains many immature cells among the mature ones, and 
the full maturity of the latter layer is attained only in a brain 
Weighing more than 1.6 grams (more than 50 days in age). 
In respect of cell size and morphological changes, the lamina 
ganglionaris and the lamina multiformis are the earliest to mature 
all the elements in them, while the lamina pramidalis matures 
more slowly, for example, and in a section from a brain twenty 
days old, we can still see many immature cells mixed with the 
mature ones in this latter layer. 
