FORM, SIZE AND WEIGHT OF THE BRAIN.
The brain possesses in a general way the form of the cranial cavity. It is applied so closely to the inner wall of the skull, that a cast of the cranial cavity repeats to a considerable degree the form of the brain. Corresponding to the numerous variations in the configuration of the skull, sometimes the brain is more spherical and at other times more ellipsoidal in form. Its dorsal surface is arched, its ventral one flattened.
The length of the brain is, on an average, between 160-170 mm. and its greatest transverse diameter 14o mm. The female brain is usually somewhat shorter than the male. The weight of the brain has long been the subject of numerous investigations. The average brain-weight of the adult man has been found to be 1375 grams, that of the adult woman 1245 grams. The minimal weight of the male brain has been placed at 96o grams, that of the female brain at 800 grams. As maximal weights, 2000 grams and over, 1900 grams, 1861 grams and 1807 grams have been specified.
The difficulty of determining the average brain-weight lies in the fact that various factors exert a substantial influence. In this connection age plays a prominent role. Observations show that the mean brain-weight in both sexes reaches its maximum towards the twentieth year, remains stationary between the twentieth and fiftieth years, and then gradually decreases. Further influences are body-weight and body-length. In general, heavier individuals possess a heavier brain and with increase in height is asso ciated increase in brain-weight ; small individuals, however, possess a relatively heavier brain than large ones. In relation to the form of the skull, a higher average brain weight has been found in the broad-headed type than in the long-headed. Many obser vations regarding the influence of race exist, with the following results : Grams.
Caucasian race : average brain-weight, 1335 Chinese : average brain-weight, 1332 • Sandwich Islander: average brain-weight, 1303 Malay and Indian : average brain-weight, 1266 Negro : average brain-weight, 1244 Australian: average brain-weight, 1185 Definite differences in the brain-weight among the European nations* have been recorded: Grams.
German : average brain-weight, 1425 English : average brain-weight, 1346 French : average brain-weight, 1280 Among all peoples, the female sex shows a smaller average brain-weight.
Further, the influence of culture is to be noted. According to the measurements of P. Broca, among the cultured nations the brain-mass probably gains somewhat in the course of time. Based on the measurements of Egyptian skulls, E. Schmidt found that nations, which have regressed from a higher culture, exhibit a smaller cranial capacity than that possessed by them during the period of their cultural bloom.
Finally, pathological conditions must also be considered, since sometimes they in duce an increase and at other times a decrease of the brain-weight.
Of great interest has always been the question, to what extent do the absolute and relative proportions of the brain indicate the favored position which man enjoys in com parison with other animals. It has long been known, that man does not possess abso
lutely the heaviest brain. The brain-weight of the elephant reaches 400o grams and more, while that of certain cetaceans may be 300o grams. It is, however, clear that, in proportion to body-weight, these animals possess relatively a smaller brain-mass than does man. On the other hand, several investigators have shown that man does not possess relatively the heaviest brain, since in this respect he is surpassed by certain song birds, apes and mice. If, however, one compares, as did Ranke, the weight of the spinal cord with that of the brain, man is found to possess the heaviest brain. While this proportion in the adult human subject is approximately 2 per cent., in the anthro poid apes this ratio increases to about 6 per cent., and among the other mammals it rises to from 23 to 47 per cent.
It is particularly difficult to establish a definite relation between brain-weight and intelligence. The comparison of many brains shows, that it is not permissible to esti mate the intellectual capacity of an individual merely according to his brain-weight. The following data exist regarding the weights of the brains of distinguished men: Grams. Grams.
Turgenjefi : 2012 Broca: 1484 Cuvier : 1861 Dupuytren : 1437 Byron : 1807 Dante : 142o Kant : 1600 Liebig : 1352 Schiller : 158o Tiedemann : 1254 Gauss: Dollinger: 1207 This comparison shows, that while the majority of these brains exceeded the average weight of 1375 grams, there are also men of eminent intellect who possess a relatively low brain-weight. Moreover, there are records of notable brain-weights (2028 and 190o grams) among individuals of insignificant mentality. Remarkably low brain weights (30o grams and less) occur among idiots.
According to the present investigations, the conclusion is justified, that psychic functions can proceed normally only where the brain-weight 11?..s passed a certain mini mum. According to Obersteiner, the lowest level to which the brain-weight may sink without noticeable impairment of the intellectual faculties is for the male brain woo grams and for the female 900.
It is to be noted, that weighing the entire brain supplies only an uncertain index of the psychic capability, for the reason that the individual parts of the brain, so varying in structure and function, do not undergo uniform increase or diminution in size and weight. An accurate knowledge of the weights of the individual parts of the brain would be of great importance, especially an exact determination of the weight of the gray substance of the end-brain, the cerebral cortex, with which particularly the higher psychic functions are associated. Even then we would fail to reach a positive result, since, in addition to the weight, other relations must be considered, especially the finer structure.