O'SHEA — ASPECTS OF MENTAL ECONOMY. 



193 



Fig. 17. — Charts showing the increase in the medullated fibres in the three layers 

 of the brain during the growing period and the decrease in advanced age. 

 Birth, to 79 years (modified from Vulpius). C, third frontal gyrus, left side; 



D, anterior central gyrus, right side; E, first temporal gyrus, left side, 



outer layer; ...., middle layer; ...., inner layer. (Donaldson.) 



12 



