1898-99.] Dr Hepburn on Improved Form of Craniometer. 611 
glabellum, would represent the prse-bregmatic segment of the 
cranial cavity.* 
The difference of an average of 1 per cent, between the prse- 
bregmatic segments of these two outstanding groups of skulls is 
equalised by a similar average difference of 1 per cent, between 
their post-lambdoidal segments. The interest, however, is largely 
associated with the parietal segment, which, notwithstanding the 
marked difference between the two groups of skulls in regard to 
the average length of the segment, viz., 97*9 mm. and 104 mm., 
yet presents an average percentage of the total length, which is 
practically identical in the two groups of skulls, viz., 55 '3 per 
cent, and 55 "5 per cent. 
From these figures it would appear probable that the greater 
length of a dolichocephalic skull, as compared with a brachy cephalic 
skull, is due to different rates of growth at the coronal and lamb- 
doidal sutures, so that while the parietal bone maintains its 
percentage proportion of the total length in each group, the gain 
of 1 per cent, in the prse-bregmatic segment and the loss of a 
similar amount in the post-lambdoidal segment determines the 
brachycephalic skull, and the reversal of the gain and loss 
characterises the dolichocephalic skull. Stated in another way we 
might say that in brachycephalic skulls growth at the coronal suture 
is in excess of, or more active than, growth at the lambdoidal suture, 
while in dolichocephalic skulls the opposite condition prevails. 
Further, the increased activity in the plane of the coronal suture is 
associated with a similar condition at the spheno-parietal and squa- 
moso-parietal sutures to enable the bregma to attain that elevation 
above the zygoma which characterises the brachycephalic skull. 
Following up the same line of inquiry it seemed advisable to 
segment the diameter of greatest length, in terms of the occipital 
condyles, for the purpose of determining the relative position of 
the condyles to the glabello-occipital diameter, since it is upon the 
condyles that the weight of the head is transmitted to the spinal 
column, and more or less balanced in the erect attitude of man’s 
progression. 
* For information with regard to the depth of the frontal sinuses, I await 
the appearance of an extremely elaborate paper which is now in course of pre* 
paration by Dr Logan Turner. 
