298 Proceedings of Boyal Society of Edinburgh. [sess. 
headed or dolichocephalic races such as the Australians the index 
should on the average he higher than in the European. This 
index, therefore, affords no proper conception regarding the degree 
of postorbital constriction. 
Another and a better method is to compare the biorbital 
diameter ( i.e . the measurement between the outer margins of the 
extremities of the two external angular processes of the frontal 
bone) with the minimum frontal diameter thus : — 
Minimum frontal diameter x 100 
Biorbital diameter 
Fronto-Parietal and Biorbital Indices. 
Min. Front. 
Dia. 
Fronto-parietal 
Index. 
Biorbital 
Index. 
Rutland specimen 
91 
61-5 
89-2 
Aberdeen , , 
97 
64*6 
88-2 
Brazil , , 
87 
61*2 
75 
This table illustrates what is said in regard to the value of these 
two indices. The fronto-parietal index would appear to indicate 
that the degree of postorbital constriction is equal in amount in 
the Rutland and Brazil specimens, and that both of these are 
relatively more constricted in this region than the Aberdeen 
specimen. An ordinary inspection by the eye is sufficient to show 
that this is not the case, and that the figures of the biorbital index 
give a much more accurate idea of the degree of cranial narrowing 
behind the orbits. The most notable feature in the Brazil skull 
is the narrowing in this region. 
In Schwalbe’s table xviii. there is no human skull which presents 
so low a biorbital index as the Brazil specimen. The average 
biorbital index for the natives of Alsace is 91*8 for the males and 
94 for the females, although there are individual cases in which it 
sinks as low as 82’9, 86*7, and 87T. In the light of this information, 
therefore, whilst it is clear that the postorbital constriction in the 
Rutland skull constitutes a marked feature, we cannot say that 
its degree is exceptional, even amongst modern European crania. 
