438 Variation and Correlation of Skull Measurements 
female skull since these two skulls show at least one significant difference, 
i. e., in the length of the nasal bone (perhaps zygomatic width also). On 
the other hand the female cranium, i. e., if we disregard the length of the 
nasal bone and zygomatic width, may be considered as an undersized male 
cranium and vice versa, since the differences observed from the three 
measurements of the cranium in the two sexes are too small to be 
significant. 
According to general belief the female brain is relatively heavier than 
that of the male although absolutely lighter. Blakeman, 05, found how- 
ever, that “The Englishman of the same age, stature and diametral 
product as the mean woman has 1235 grs. brain-weight, or only 10 grs. 
more than the average woman. The Englishwoman of the same age, 
stature, and diametral product as the mean man has 1315 grs. brain- 
weight, or only 13 grs. less than the average man.” He concludes from 
the above that “as far as present evidence goes, we can safely conclude 
that there is no sensible relative difference in the brain-weights of man 
and woman, the absolute differences observed are quite compatible with 
the differences which result from the relative size of the two sexes.” The 
same conclusion, as has been given by Blakeman, may be drawn from the 
present study on the albino rats. It was found (see Table X) that 
when the length of the entire skull of the male rat is equated into the 
length of the entire skull of female, and vice versa, the resulting values for 
the cranial capacity in the two sexes are almost identical. The difference 
is in average less than 0.5 per cent, indicating that the sexual difference 
found in the cranial capacity is entirely accounted for the difference in 
the size of body. It is also interesting to note in our case that only one 
character has been equated and therefore if we took a multiple regres- 
sion-equation the difference would probably almost disappear. 
(g) Characteristic equations——I have put together on the opposite 
page all characteristic equations which have been used in the course of 
the present study. Equations 1-14 will enable us to find the probable 
values of the other characters of the skull in two sexes when we know the 
length of the entire skull, while from the equations 15 and 16 we can 
obtain the probable brain-weight from the observed body-weight. 
The characteristic equations show clearly that the relation between the 
length of the entire skull and the other characters of the skull, and brain 
and body-weight can not be determined by simple arithmetical proportion 
but require in each case the introduction of two or more of the necessary 
constants which are specific for the character chosen. It follows therefore 
that in general if the relation existing between the two characters turns 
