Method o f
determining
Prognathism
adopted.
Cranial
Capacity.
The method
of estimating
it
adopted.
from the nasion, and by employing our scale of prognathism (see ante, p. 42) to record
the extent of facial projection. In the trigonometer which we have employed (Plate 1)
this scale has been engraved on the instrument, so that when dealing with the triangles
reduced to their proportions (of base bn= ioo) it has been possible at one operation to
determine the degree of prognathism according to our scale. The same results may
be obtained by the use of the diagram on p. 42 and the employment of a suitable
protractor.
As not only the three absolute measurements but also the gnathic angle, Flower’s
alveolar index, and the resulting classification of every specimen are published in an
Appendix, the reader can readily test the system and his own application of it.
With regard to the cranial capacity, we were anxious to ascertain whether or no
during the centuries throughout which our periods range there had been any perceptible
increase in the bulk of the cranial contents, correlated possibly with associated changes in the
head form. At the time at which the specimens were examined it was considered too
hazardous to subject them to the process of cubage, however delicately employed, and
consequently we have no such records to submit. A number of the specimens- which were
sent to Oxford, and which were treated with gelatine, have been cubed with mustard-seed,
and the results are interesting as enabling us to compare the measures taken with those
which were obtained by estimate. Not having had individual experience in regard to
this matter we had recourse for purposes of estimation to the formula
Max. Length x Max. Breadth x Basi-bregmatic Height
suggested in Topinard’s Anthropology, p. 680, which is based on the assumption that the
cranial cavity may be considered as equal to half the capacity contained by an ellipse
having the said diameters. In comparing the fifty-one specimens of which we were able
to take the cubage with the capacity estimated by this means, we found that in over 50 per
cent the variation of the estimate in excess or defect of the cubage was not more than
30 cubic centimetres, and in only 8 per cent, did it exceed 70 cubic centimetres, whilst in
12 per cent the figures were identical by either method. On these grounds it appeared
to us that the results were sufficiently accurate to form a basis for broad generalizations.
Accordingly the estimated cranial capacity of the 1,500 odd specimens has been calculated
in this way and recorded in the catalogue given in the Appendix.
A1B\C\D\E
PLATE I. Trigonometer for estimating Projection of Face.
[F o r instructions as to use see page 43.J