This is a measurement of much value, both alone and as a supplement to
the cranial index, for skulls with the same index may be high or low
and thus really of a radically distinct type.
The height of the vault is best studied in its relation to the other
cranial dimensions, particularly to the mean of the length and breadth,
with both of which it correlates. But in the Eskimo it is also of
interest to compare the height with the breadth of the skull alone.
The former relation is known as the mean height index and the latter
as the height-breadth index. Both mean the percentage value of the
basion-bregma height as compared to the other dimensions.
The mean height index H/(Mean of L+B), advocated independently by the
writer since 1916 (Bull. 62, Bur. Amer. Ethn., p. 116), is proving
of much value in differentiation of types and has already become
a permanent feature in all writers' work on the skull. There is a
corresponding index also on the living.
In the American Indian the averages of the index range from
approximately 76 to 90. (See Catalogue of Crania, U. S. Nat. Mus., Nos.
I and II.) Where the series of specimens are sufficiently large the
index does not differ materially in the two sexes. Indices below 80 may
be regarded as low, those between 80 and 84 as medium, and those above
84 as high.[153]
The southwestern and midwestern Eskimo skulls show mean height indices
that may be characterized as moderate to slightly above medium. In
general the broader and shorter skulls show lower indices, approaching
thus in all the characters of the vault the Mongolian skulls of Asia.
(Compare Catalogue Crania, U. S. Nat. Mus., No. I.) The Indian Point,
St. Lawrence Island, and Little Diomede Island skulls are again, as
with the cranial index, very close together, strengthening the evidence
that the three constitute the same group of people. (Pls. 59, 60.)
The northwestern Eskimo and most of those of the northeast have
relatively high vault. Barrow and Point Barrow are once more almost
the same. The Point Hope group shows a high vault, though also rather
broad. The somewhat broad Hudson Bay crania are but moderately high,
like those of the southwestern Eskimo. The northern Arctic skulls give
smaller height than would be expected with their type; the Southampton
Island specimens give higher. The old Igloo group from near Barrow
stands again close to Greenland; its skull is even a trace narrower
and higher, standing in both respects at the limits of the Eskimo.
The whole, as with the cranial index, shows evidently a rich field of
evolutionary conditions.