In many savage tribes there are artificial deformations of the skull, which render it useless as a means of comparison. The “Flathead Indians” are an example, and many Peruvian skulls are thus pressed out of shape. It is singular that this violence to such an important organ does not seem to be attended with any injurious result on the intellectual powers.

The orbit of the eyes is another feature which varies in races. The proportion of the short to the long diameter furnishes what is known as the “orbital index.” The Mongolians present nearest a circular orbit, the proportion being sometimes 93:100; while the lowest range has been found in skulls from ancient French cemeteries, presenting an index of 61:100. The latter are technically called “microsemes;” the former “megasemes,” while the mean are “mesosemes.”[6]

In a similar manner the aperture of the nostrils varies and constitutes quite an important element of comparison known as the “nasal index.” Where this aperture is narrow, the nose is thin and prominent; when broad, the nose is large and flat. The former are “leptorhinian,” the latter “platyrhinian,” while the medium size is “mesorhinian.” This division coincides closely with that of the chief races. Almost all the white race are leptorhinian, the negroes platyrhinian, the true Asiatics mesorhinian. The Eskimos have the narrowest nasal aperture, the Bushmen the widest.

The projection of the maxillaries, or upper and lower jaws, beyond the line of the face, is a highly significant trait. When well marked it forms the “prognathic,” when slight the “orthognathic” type. It is much more observable in the black than in the white race, and is more pronounced in the old than in the young. It is considered to correspond to a stronger development of the merely animal instincts.

The relation of the lower to the upper part of the head is measured mainly by two angles, the one the “maxillary,” the other the “facial” angle. The former is the angle subtended by lines drawn from the most projecting portion of the maxillaries to the most prominent points of the forehead above and the chin below. (The angle M G S in the accompanying diagram, Fig. 4.) This supplies data for two important elements, the prognathism and the prominence of the chin. The latter is an essential feature of man. None of the lower animals possesses a true chin, while man is never without one. The more acute the maxillary angle, the less of chin is there, and the more prognathic the subject. The averages run as follows:

The European white160°.
The African negro140°.
The Orang-outang110°.

Fig. 4.—Lines and angles of skull measurement.

The facial angle is that subtended by the same line, from the most prominent point of the upper jaw to the most prominent part of the forehead, and a second line drawn horizontally through the center of the aperture of the ear. (The lines M G, D N.) It expresses the relative prominence of the forehead and capacity of the anterior portion of the brain. The more acute this angle, the lower is the brain capacity. The following are its averages:

The European white80°.
The African negro70°. to 75°.
The Orang-outang40°.