GROWTH OF THE CEREBRAL CORTEX 255 
TABLE 7 
Giving the average cortical thickness of man, arranged according to age and sex, 
together with the brain weight. Quoted from Donaldson (’91) 
AGE BRAIN WEIGHT AVERAGE CORTICAL THICKNESS 
Males 
years | grams mm. 
35 1419 2.81 
35 1443 2.98 
39 1393 2.82 
45 1367 | 2nO2 
57 1464 2.94 
1 1210 Beli 
Females 
40 1196 2.74 
45 iil} 2.90 
uy 1312 3.07 
Average 
1331 2.92 
weeks, washing in water for twenty-four hours, 95 per cent alco- 
hol for two days, final preservation in 80 per cent alcohol, and 
imbedding in celloidin. The sections were cut about 100 micra 
thick and measured unstained under a low magnifying power 
with a micrometer eyepiece, at the summit of the gyrus and at 
the side, midway between the summit and the bottom of the 
bounding suleus. To obtain the average thickness at the lo- 
cality, the smaller figure was multiplied by 2, added to the larger 
figure, and the sum divided by 3 
Table 7 shows the average pnbh aes of the cortex (taken from 
the fourteen localities) arranged according to sex and age, 
quoted from Donaldson (’91). If we take the nine cases in this 
table as the basis for computation, we find the mean thickness 
of the cortex to be 2.92 mm., with a probable error of the mean 
equal to +0.026 mm. 
I wish to cite also the average thickness of the cortex, as thus 
obtained by Donaldson (’91), according to locality (table 8). 
These localities are shown in figure 3 and the relative thickness 
