1898 - 99 .] Dr Hepburn on Improved Form of Craniometer. 613 
panzee 46 - 7 per cent. No doubt in all of these apes the develop- 
ment of the frontal sinuses, superciliary ridges, and occipital 
crests may account for a considerable amount of the difference 
between the two segments. Nevertheless it is quite evident that a 
very pronounced alteration occurs in the relative proportions of 
the prse- and post-condyloid segments of the glabello-occipital 
length as we ascend from the anthropoid ape to man. In other 
words, there is an adjustment of the balance of the skull upon the 
atlas in association with the assumption of the erect attitude. 
Prof. Cleland* has directed attention to the balance of the skull 
upon the vertebral column, and believes that its position in man 
results from the increasing prominence of the anterior extremities 
of the occipital condyles, whereby the skull is tilted upwards and 
backwards, the tilting of the skull being complicated by the in- 
crease in cranial curvature which proceeds from growth. He also 
points out that the falling forward of the skull in old age is due to 
the reduction in the size of the front ends of the occipital condyles. 
Without attempting to criticise or traverse this argument, and 
while admitting the value and accuracy of the observations, I 
nevertheless think that the measurements which I have recorded 
show proportions between the prse-condyloid and post-condyloid 
segments of the glabello-occipital length which could not result 
merely from increased prominence of the occipital condyles, nor be 
affected by their partial absorption. It appears probable that 
varying rates of growth for the different sections or bones which 
contribute to the formation of the antero-posterior arch of the 
skull result in an increase of the occipital section, and therefore 
the condyles are proportionately moved forwards in relation to the 
base of the skull and the glabello-occipital diameter. 
An examination of a number of skulls will show that a line 
drawn transversely between the centres of the two external 
auditory meatuses occupies a variable position with regard to the 
plane of the anterior margins of the occipital condyles. This is 
true not only of human skulls, but also of the skulls of other 
mammals. In order to obtain facts for comparison I segmented 
the glabello-occipital length in terms of the centre of the external 
auditory meatus. 
Cleland, loc. cit. 
