CENTRAL NERVOUS SYSTEM. 719 



away by horizontal sections as far down as the tentorium. The parts of the 

 hemispheres still remaining were then removed by a section passing in front of 

 the quadrigemina. The cerebellum was next separated from the stem, this 

 latter being represented by the quadrigemina, the pons, and the bulb. Each 

 hemisphere, the cerebellum, and the stem were then weighed separately. 



Between the twentieth year and old age there are here represented the average 

 encephalic weights, arranged in two main groups according to sex, and then in 

 large horizontal groups according to stature, those of a given stature being sub- 

 divided according to age. This record is typical of what has been found by 

 other observers and may be discussed without further evidence. 



If groups of similar ages and corresponding statures are compared accord- 

 ing to sex, it is at once seen that the male possesses the heavier encephalon, and 

 that all the subdivisions of it are likewise heavier. 



When individuals of the same sex and falling within the same age-limits 

 are compared according to stature, those having the greater stature are found to 

 have the greater brain-weight, though in the case of the subdivisions of the 

 encephalon, and especially among the females, there are some irregularities, but 

 these would probably disappear could the number of observations be increased. 

 Finally, within the groups of those having the same stature, but different ages, 

 the weight decreases with advancing age. The middle group, forty-one to 

 seventy years of age, is in one way unfortunate, because, while the brain is 

 probably still growing (see curve of growth, Fig. 204), during the first third 

 of that period, and is nearly stationary (males especially) during the second, it 

 begins to diminish so rapidly during the last third that the average weight is 

 lower for the cases between sixty-one and seventy years than for the twenty 

 years between forty-one and sixty years. Between seventy-one and ninety 

 years the involutionary changes in the central system are most marked, and 

 the decrease in weight during this period is clearly indicated. 



Body-weight. As regards the relations between the weight of the central 

 system and the weight of the body the case is not so clear. In the first place, 

 the presence of fat at maturity disturbs the results, because the nervous system 

 cannot be expected to vary with changes in the quantity of an inactive tissue 

 representing stored food-stuff merely. The taller individuals have a larger 

 cranial capacity than the shorter, and hence the variation of brain with body- 

 mass can only be made fairly when persons of the same stature, but of dif- 

 ferent body-weights, shall have been carefully compared. 



If under these circumstances it shall appear that the bulkier individuals 

 have the heavier nervous system, then the excess in their favor can be fairly 

 correlated with the excess of the active tissues. 



Before suggesting an explanation of these variations according to age, sex, 

 and stature, it is to be noted that they occur in other mammals as well as in 

 man. As regards the difference in the weight of the encephalon due to sex, it 

 has been shown to obtain among the apes, 1 the male having the heavier brain . 

 and from the general relation of size according to sex among the mammalia, 

 1 Keith : Journal of Anatomy and Physiology, 1895. 



