178 THE CEREBRAL HEMISPHERES. 



average thickness for any locality. But beyond the fact that the cortex is somewhat 

 thinner near the hemisphere-poles, and especially the occipital pole, than in the 

 intermediate parts, no definite statement regarding the relative thickness of different 

 parts can at present be made. Females have a very slightly less thickness of cortex 

 than males (less than 1 per cent.), and the right hemisphere less than the left : the 

 difference may amount to 7 per cent. (Donaldson). 



Weight. The results obtained by Sims, Clendinning, Tiedemann and J. Eeid 

 showed the maximum weighb of the adult male brain, in a series of 278 cases, 

 to be about 1810 grammes (04 oz.), and the minimum weight about 960 grammes 

 (34 oz.). In a series of 191 cases, the maximum weight of the adult female brain was 

 1585 grammes (56 oz.). and the minimum 880 grammes (31 oz.). In a very large 

 proportion the weight of the male brain ranges between 46 oz. and 53 oz., and 

 that of the female brain between 40 oz. and 47 oz. Similar statistics have been 

 published by Peacock, R. Wagner, Bischofl', Huschke, Boyd, "Weisbach and others. 

 The mean weight at from 20 to 40 years of age was found by Boyd to be 48 oz. 

 (1360 grammes) for the male, and 43| oz. (1230 grammes) for the female brain. 

 Although many female brains exceed in weight particular male brains, as a general 

 fact it may therefore be affirmed that the adult male encephalon is on an average 

 heavier by 4 oz. or 5 oz. than that of the female (or about 9 per cent.). 



The appended table, which has been compiled from the observations of E. Boyd 

 (Phil. Trans. 1860), shows in grammes the mean weights at different ages in the 

 two sexes. 



MALES. FEMALES. MALES. FEMALES. 



It would appear from the above that the brain is absolutely heavier between 14 

 and 20 years of age than at any other period of life, and that at the age of 80 it has 

 lost about 90 grammes, or rather more than 3 ozs., i.e., about -^ of its whole weight. 



The figures obtained by Broca are somewhat higher than these, e.g., between the 

 ages of 30 and 35, in the male, an average of 1421 grammes (50 oz.) ; in the 

 female, 1269 grammes (45 oz.). According to the same statistics, the weight of the 

 brain attains its maximum, not before the age of 20, as found by Boyd. but between 

 25 and 35 in the male and a little earlier in the female. This agrees with the 

 results of Peacock. 



The two hemispheres of the same brain, although hardly ever of exactly the 

 same weight, show no constant difference, the one half preponderating just about as 

 often as the other, and the average difference being only about 5 grammes (Braune). 

 There is no evidence that the right hemisphere is the heavier in left-handed people. 



It has frequently been found that the brains of distinguished men have a brain -weight 

 above the average, sometimes markedly so, bat the rule has many exceptions. The converse 

 is by no means true. 



The relative weight of the encephalon to the body is liable to great variation ; 

 nevertheless, the facts to be gathered from the observations of Clendinning, 

 Tiedemann, and Reid, furnish the following general result. In a series of 81 males, 

 the average proportion between the weight of brain and that of the body at the ages 

 of twenty years and upwards, was found to be as 1 to 36'5 ; and in a series of 82 

 females, to be as 1 to 36'46. The results of Bischoff's observations give 1 to 35'2 in 



