206 



THE GROWTH OF THE BRAIN. 



the larger square, or one-half the area of the smaller 

 one, and is the proportion of the cortex exposed on 

 the outer surface of the hemispheres. In the tables 

 by Wagner the relative development of the cortex in 

 the two hemispheres was noted, and it was found to 

 be more extensive on the right side in the case of 

 Fuchs and Gauss, whereas in the woman and labour- 

 ing man that of the left side was greater. In dealing 

 with the extent of the cortex by methods of direct 

 measurement, its thickness was not determined, and the 

 earlier investigators were ready to admit that an im- 

 portant datum was therefore lacking. Since that time, 

 however, a number of elaborate investigations on the 

 thickness of the cortex have been made. The method 

 of determining the average thickness of the cortex is to 

 measure samples of this layer from a large number of 

 localities and then fuse the results. The accompanying 

 table, giving the figures obtained by the principal investi- 

 gators, shows that the different observers are by no 

 means in accord. 1 



TABLE 50. SHOWING THE AVERAGE THICKNESS OF THE 

 CORTEX IN BOTH SANE AND INSANE PERSONS AS DETP;R- 

 MINED BY DIFFERENT INVESTIGATORS. (Donaldson.} 



1 Donaldson, Am. Journ. of Psychology, 1891. 



