208 THE GROWTH OF THK BRAIN. 



place a thinner cortex in the cases of mental disease 

 Among normal individuals my own figures, obtained 

 from the so-called American brains, show the greatest 

 thickness. Comparing the two hemispheres in the same 

 brain series, it is found that the difference is extremely 

 small, and that the figures hardly permit of the inference 

 that either the right or the left hemisphere has normally 

 the thicker cortex a conclusion similar to that reached 

 concerning the comparative weights of the two hemi- 

 spheres. When, however, the average thickness in the 

 brain of the males is compared with that of the females, 

 there is in every instance a slight advantage in favour 

 of the males. The constancy of this difference indicates 

 that probably the cortex in the female brain is on the 

 average thinner than that of the male ; just as on the 

 average the female brain weighs somewhat less than 

 that of the male. I give here a curve (Fig. 39) which 

 shows the average thickness of the cortex at the locali- 

 ties indicated on the accompanying outlines. In general 

 the cortex is thickest on the convex aspect of the hemi- 

 sphere, and thinnest on the ventral and mesal. It is 

 also thicker in the middle of the hemispheres than at 

 the poles. 



The change in the architecture produced by growth 

 and the significance of the constructional elements in 

 the general arrangement of the central system form a 

 separate line of investigation : to these matters the next 

 chapter will be devoted. 



