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Mass And Weight Of The Brain

average weighed brains

MASS AND WEIGHT OF THE BRAIN. - The human brain is absolutely bigger and heavier than the brain of any animal, except the elephant and the larger whales. It is also heavier relatively to the bulk and weight of the body than are the brains of lower animals, except in some small birds and mammals. Considerable variations, however, exist in the size and weight of the human brain, not only in the different races of mankind, but in individuals of the same race and in the two sexes. The heaviest brains occur in the white races. The average weight of the adult European male brain is 49 to 50 oz., that of the adult female 44 to 45 oz. ; so that the brain of a man is on the average fully 10 per cent. heavier than that of a woman. The greater weight of the brain in man as compared with woman is not in relation merely to his greater bulk, but is a fundamental sexual distinction ; for, whilst there is a difference of 10 per cent. in the brain weight, the average stature of women is, as Thurnam has calculated, only 8 per cent. less than that of men. Dr Boyd states that the average weight of the brain in the newly born male infant is 1 1 •67 oz.; in the female only 10 oz. The exact age at which the brain reaches its maximum size has been variously placed at from the 3d to the 8th years by different authors ; but it continues to increase in weight to 25 or 30, or even 40. After 60 the brain begins to diminish in weight ; in aged males the average weight is about 45 oz., in females about 41 oz. In some cases the adult brain considerably exceeds the average weight. The brains of several men distinguished for their intellectual attainments have been weighed : the brain of Olivier weighed 64i oz.; of Dr Abercrombie, 63 oz.; of Professor Goodsir, 57-12 oz.; of Spurzheim, 55 oz. ; of Sir J. Y. Simpson, 54 oz. ; of Agassiz, 53'4 oz. • and of Dr Chalmers, 53 oz. But high brain weights have also been found where there was no evidence of great intellectual capacity. Peacock weighed four male brains which ranged from 62'75 to 61 oz.; Boyd, a specimen of 60.75 oz.; and Turner has recorded one of a boy aged fifteen which weighed GO oz. In the brains of the insane high brain weights have also been observed. Bucknill met with a brain in a male epileptic which weighed 64i oz. • Thurnam, one which weighed 62 oz.; and in the West Riding Asylum, out of 375 males examined, the weight of the brain in 30 cases was 55 oz. or upwards, and the highest weights were No reliable determinations have as yet been made of the exact proportion, as regards bulk and weight, which the convolutions bear to the corpora striata, optic thalami, and corpora quadrigemina, but data are obtainable of the relative weight of the pons, cerebellum, and medulla to the entire encephalon. Between the ages of 20 and 70 the ratio of weight of the pons, cerebellum, and medulla, to the entire brain, is as 13 to 100, and this relative weight is virtually the same in both sexes.

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