DR. J. CLELAND ON THE VARIATIONS OF TIIE HUMAN SKULL. 
141 
Distance of the arch at various points from the base (General Table, columns 33 to 39). 
— To estimate the distance from arch to base in different parts of the mesial extent of 
the skull four diameters have been chosen, namely, a line from the level of the foramen 
opticum to the fronto-parietal suture, which may be termed the frontal depth, and three 
lines converging to the spheno-occipital suture from the midparietal point, occipito- 
parietal suture, and the occipital tuberosity, which may be termed respectively the 
parietal, occipito-parietal, and occipital depths. In comparing them the parietal depth 
has been chosen as the standard, not merely because it is the longest, but because, as 
may have been observed from what has been already stated with respect to the angles 
connected with the arch, it may be regarded as an axis behind and in front of which the 
arch of the skull expands in growth from birth onwards. 
In the first four foetal skulls the frontal depth is such as would be esteemed high in 
the adult, but in the two skulls of the eighth month it is low, and in the skulls of infants 
it is still lower ; in childhood, however, it rises and appears to gain the adult proportion. 
The occipito-parietal and occipital depths are on an average slightly smaller in the foetus 
than in the infant, and both, but more especially the occipital, increase in childhood. 
These measurements, like those which have gone before, show that the sugar-loaf-like 
form of the infant skull is no mere mechanical result of compression during birth, but 
is prepared beforehand, and subsequently lost in the proper process of growth. 
As in the case of other measurements, so also with those under consideration, the 
results in the adults of different nations are not altogether distinct at first sight ; and it 
must be owned that on them alone a speculation could not be based with regard to the 
nationality of a particular skull ; but by taking averages in those instances in which 
several skulls have been examined, national differences are indicated of a not altogether 
uninstructive kind. Comparing fourteen different races together (some of them repre- 
sented, however, by only one or two specimens), and marking as high, moderate, or low 
the proportionate lengths of the frontal, occipito-parietal, and occipital depths as com- 
pared with the parietal depth, the following results are obtained : — 
MDCCCLXX. 
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