H. Wagner has estimated the surface of the cerebral hemispheres, by covering them with goldleaf, to be equal to from 187,00o-221,000 sq. mm. (2.1-2.5 sq. ft.): this of course represents the extent of cerebral cortex. The cortex varies in thickness from 1.55 mm. in the floor of the small polar sulci to 5 mm. in the superior end of the central gyri. The average is 3 mm. In all regions, the depth is greater in the summit of a gyrus than in the bottom of a sulcus. It is slightly thicker in the left hemisphere and in the male brain. Investing the white substance, its weight comprises so per cent. of the entire hemisphere, though the specific gravity of the cere bral cortex is 1033 (r029-1038) and that of the cerebral white substance 1041 (1036-1043). The specific gravity of the entire brain is 1036.
The average weight of an adult white man's brain is about 1375 gm. (48.5 oz.), An adult white woman's brain averages 1245 gm. (43.9 oz.). After sixty years, the brain weight diminishes gradually to the extent of 6 or 7 per cent. E. A. Spitzka has found the average brain weight of 108 distinguished men to be 1473 gm.; and he found the beginning of senile atrophy in these men to be postponed to years on an average. Villiger gives the average weight of the German brain, 1425 gm.; the English brain, 1345 gm.; and the French brain, 1280 gm. Most of these were obtained from dissecting room specimens.
E. A. Spitzka's findings in 108 distinguished men (Trans. Am. Phil. Soc., 1908): Average brain weight in grams 27 Americans (U. S. and Canada) 1519 14 British and Scots zo French 1456 • 38 Germans and Austrians 1439 Grand average. .75 9 of various nationalities with nearly the same average.
According to the estimate of Meynert the brain is made up as follows: 78.5 per cent. fore-brain; It per cent. mid-brain, pons and medulla, and 10.5 per cent. cerebellum.
Cerebrum equals seven-eighths of the brain, rhombencephalon one eighth. In a male brain of 1375 gm. cerebrum weighs 1204 gm. (42.5 oz.); cerebellum, 143 gm. (5 oz.); and pons and medulla, 28 gm. (1 oz.). The female cerebrum weighs 1074 gm. (38 oz.); cerebellum, 143 gm. (5 oz.); and the pons and medulla, 28 gm. (r oz.), in a brain weighing
1245 gm.
The brain attains almost its full weight in the first six years; but it con tinues to increase slightly through youth and manhood up to thirty-five or forty years. Education and experience increase it appreciably and they contribute greatly to the complete development and medullation of the neurones and to the establishment of those mechanims necessary to the functions of the nervous system in man.
At birth the male brain weighs about 400 gm. (14.2 oz.) the female brain, 38o gm. (13.4 oz.). These weights are doubled in a year and in six years they are thrice the weight at birth.
The relation of brain to body-weight in the new born is about t to 8, in the adult about t to 5o. Tiedemann, gives the larger proportions: at birth, male, i to 5.85, female, i to 6.5; adults who died without wasting disease, x to 41.
Some over-sized brains from distinguished men: Prof. Gauss, 1492 gm.; Prof. Agassiz, 1512 gm.; Daniel Webster, 1516 gm.; Kant, the philoso pher, 1600 gm.; Thackeray, 1658 gm.; Cuvier, 1861 gm.; Ivan Turgenef, 2012 gm.
Cranial capacities Cranial capacities (Spitzka) in (Spitzka) in cubic centimeters cubic centimeters Daniel Webster 1999.5 Dante 1493 Kant. 1740 Bach. 1480 Franz Joseph Gall 1692 DesCartes 1706 Beethoven 175o Subnormal brain-weights from celebrated men: Dr. Leibig, 1352 gm.; Gambetta, the French statesman, 1294 gm.; Walt Whitman, 1282 gm.; Dr. Tiedemann, 1254 gm.; Dr. DoRinger, 1207 gm.; Dr. Franz Joseph Gall, the phrenologist, 1198 gm.
J. Wiglesworth and George A. Watson report an epileptic dement who had a head measuring 25 inches in circumference and a brain weighing, with the pia and arachnoid, 213o gm. (Brain, Vol. 36, Part I, p. 31).
The elephant has a brain, in some cases, weighing 4000 gm., and the large whales one weighing 300o gm. The gorilla has one-third as much brain as man. A Borneo monkey (Macaccus maurus) has a brain weighing 115 gm. The gorilla and monkey show marked deficiency of the frontal lobes, when compared with man (Figs. 22 and 24). The elephant's and whale's brains are surely made up chiefly of motor and sensory mechanisms, the psychic regions being very small.