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Brain Measurements and Weights

weight, gm, size, capacity, lobe and body

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BRAIN MEASUREMENTS AND WEIGHTS Ethnologic investigations of cranial capacity and brain weight reveal two important general facts: first, the cultured and aggressive races possess the larger brains; and, second, the cranial capacity increases during the rise from barbarism to culture and power and, conversely, decreases with the decline of a people. The former fact is illustrated by the findings of Davis (Phil. Trans., 1868) who estimated brain weight from cranial capacity. He gives the average brain weight in the different races as follows: Cauca sian, 1335 gm.; Chinese, 1330 gm.; Sandwich Islanders, 130o gm.; Malays and North American Indians, 1265 gm.; Hindus, 11go gm.; and Aus tralian Natives, 1185 gm. Secondly, the brain of prehistoric man, as repre sented by the "Neanderthal skull," weighed about r000 gm. The "Trinil skull" contained a brain estimated at Boo gm. Again, E. Schmidt has discovered that the cranial capacity is smaller in the modern Egyptians than in the mummy skulls of the Ptolemaic period when Egypt was in her prime.

It is also observed that the brains of great men are usually above the average size (E. A. Spitzka) and that a very diminutive brain (below goo gm.) is never associated with high mentality and is found often in imbe ciles and idiots. Hence, there is some ground for the popular belief that the size of the brain has a direct relation to mental capacity; but such a broad inference is not warranted by other facts. Indeed, a brain near the average size and weight, possessing some degree of frontal lobe predomi nance, is most often associated with superior moral and mental attributes. The area of the frontal lobe should exceed slightly the combined areas of the parietal and temporal lobes in brains of high types, according to H Wagner (Figs. as and 24). Compare the brain surface of the great mathematician, Prof. Gauss, with that of an ordinary man, a workman.

These measurements of H. Wagner and others indicate that the relative size of the frontal lobe is of prime importance to mental capacity; and such a conclusion is further supported by the facts that imbeciles and idiots are especially deficient in the frontal lobe, that the grade of senile dementia is proportionate to the amount of degeneration in this lobe, and that pre dominance of the frontal lobe is characteristic of the step up from the highest animal to man. But surely the perfection of individual neurones

contained in the brain and the completeness of their contact relations are of far more significance than mere size and weight. Quality is of first im portance; that being present, then, quantity may signify. Physiology has shown that the character of circulating fluids, also, must be taken into account (Figs, 22, 23 and 24).

Brain dimensions and weight vary with stature and weight of body. As a rule, the larger body contains the larger brain; but, as the increased bulk of body only necessitates increase of the motor and sensory mechanisms (and not of the higher psychic mechanisms) the relative size of the brain is lower in men of large stature and weight than in men of average size. Attempts have been made to show that of all animals man has the largest brain when it is compared with the weight of the body. They failed. The Gibbon, in this respect, has a brain equal to man's, certain apes have a greater brain relatively, and some very insignificant animals have a higher ratio of brain to body than man.

Cranial configuration influences both brain measurements and weight. The dolichocephalic brain with its long polar and short equatorial axis usually possesses smaller area of cortex and lower weight than the brachy cephalic brain in which the two axes are more nearly equal.

The occipito-frontal axis of the male brain measures from 160-17o mm. (6.4-6.8 in.); of the female brain, 150-160 mm. (6-6.4 in.). The great est transverse diameter is the same in both sexes, 140 mm. (5.6 in.). The average vertical height in both sexes is 125 mm. (5 in.). The female brain, though shorter, is equal in breadth and depth to the male brain.

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