IN THE DIFFEEENT EACES OE MAN. 
507 
It has already been stated that the 15 per centum tare is intended to cover the weight 
of the dura mater and pia mater, the arachnoid, the fluids of these membranes and of 
the ventricles, and also of the blood contained in the large vessels. This weight alto- 
gether is considerable. Professor Marshall has made the following explanatory remarks. 
“ If the brain, in its natural state, filled the cranial cavity as completely as water will 
afterwards, it would be easy, by taking the specific gravity of nervous substance as com- 
pared with water, to estimate the quantity of brain which once occupied any given skull ; 
but the fact that this is not the case, especially in regard to the base of the brain, and 
the difficulty in determining the weight of the membranes, the amount of blood which 
the vessels may contain, and the quantity of cerebro-spinal fluid which fills the ventricles 
and all otherwise unoccupied spaces, render it impossible thus to arrive at so definite an 
estimate as in the other way,” i. e. by weighing the encephalon* *. 
The present may be regarded as the first attempt to deduce with accuracy the weight 
of the brain from the capacity of the skull, on any commensurate scale. Professor 
Tiedemann’s and Professor Morton’s crude observations are of small value in this respect, 
and the attempts of others have been very limited and uncertain. It is remarkable that 
neither of these two accomplished men made any allowance in their observations for the 
membranes and fluids. This might not be deemed necessary in the comparison of the 
relative size of the cranial cavity in different races, aimed at by the former, who, when 
he subjected the brain to the weighing process, divested it of the arachnoid and the 
pia mater. The latter observer might seem to have overlooked the need of any allow- 
ance ; at all events, in his Memoirf , he tells us that by his process of gauging the cavity 
of the skull with leaden shot, “ I thus obtain the absolute capacity of the cranium, or 
bulk of the brain, in cubic inches ; ” and he describes his great Table as “ showing the 
size of the brain in cubic inches ” — whereas, in fact, it merely gives the capacity of 623 
crania in cubic inches. It is quite needless to endeavour to prove that an allowance for 
membranes and fluids is absolutely necessary. 
Attempts have been made by different observers to determine the proportion in weight 
by which the brains of men exceed those of women. This appears to be variable, 
and possibly the variation may be in relation to particular races ; but to decide this 
question would require materials of a very exact nature. The proportion differs from 
about 5 per cent, in our Australians, to more than 10 per cent, in our Tasmanians. It 
may be said generally in our series to range from less than 10 per cent, to something- 
more than 12^ per cent., so that the proposal of Professor Welcker to regard it as 10 
per cent, may for the present be as safe as any other. 
When Professor Tiedemann considered as the result of his investigation, that he was 
closely coincide. Eor reasons already given, it is apparent that no rule can be formed -which shall agree with 
all individual cases. 
* John Marshall, F.R.S., “ On the Brain of a Bushwoman,” &c., Philosophical Transactions, 1864, p. 506. 
t Proceedings of the Academy of Natural Sciences of Philadelphia, October 1849. 
