Anthropological Survey in Alaska

The next table gives the percentage relations of the basion-nasion diameter to the mean diameter of the skull. The correlation of the two is even closer than in the case of the skull length, and the grouping, while in the main alike, seems in general even more in harmony with that in previous comparisons. The St. Lawrence Island females are very exceptional, as was also apparent in other connections. The unusual smallness of their skull (compare section on Cranial module) is evidently due to a poor development of its posterior half.

PROGNATHISM

Since better understood, the subject of facial prognathism has lost much of its allure in anthropology; yet the matter is not wholly without interest.

Facial protrusion is as a rule secondary to and largely caused by alveolar protrusion, which in turn is caused by the size and shape of the dental arch; and the dental arch is generally proportional to the size of the teeth. The form of the arch is, however, quite influential. With the teeth identical in size a narrow arch will be more, a broad arch less protruding, and a narrow arch with small teeth may protrude more than a broad one with larger teeth. Another influence is that of the height of the upper face, the same arch protruding more in a low face than in a high one. And still another factor is the incline of the front teeth, though this affects merely the appearance of prognathism and not its measurements.

There are different ways of measuring facial prognathism, and with sufficient care all may be effective; I prefer, for practical reasons, linear measurements from the basion, which, together with the facial and subnasal heights, give triangles that can readily be reconstructed on paper and allow a direct measurement of both the facial and the alveolar angle. The three needed diameters from basion are taken, the first to the "prealveolar point," or the most anterior point on the upper dental arch above the incisors; the second to the "subnasal point," or the point on the left (for convenience) of the nasal aperture, where the outer part of its border passes into that which belongs to the subnasal portion of the maxilla (the point where the subnasal slant begins); and the third to nasion. The facial height is that from the alveolar point (lowest point of the upper alveolar border in the median line) to nasion; while for the subnasal height, which can not be measured directly, I utilize the difference between the facial and nasal heights, which is very close to the needed dimension.

The important basion-nasion diameter has already been considered. That to the subnasal point needs no comment. That to the prealveolar point shows in the western and other Eskimo as follows:

As in other details, so here there is a remarkable similarity between the skulls from the three large areas, pointing both to the unity of the people and to absence of heterogeneous admixtures. As the skull length increases so does the basi-alveolar line, but the relative proportions of the two remain very nearly the same.

The relative value of the basi-alveolar length in the males, compared to the length of the skull, is in general about 0.5 per cent higher than it is in the females. This is just about the excess of the relative proportion of the length of the male dental arch when compared to the same skull dimension. The general mean skull length in the Eskimo male approximates 18.705, in female 17.899 centimeters; the mean length of the arch is, in the male, close to 5.625, in the female 5.365 centimeters; and the percentage relation of the latter to the former is 30.6 in the males, 30 in the females. The relatively slightly greater basi-alveolar length in the males is evidently, therefore, at least partly due to the relatively longer male dental arch, which in turn is doubtless due to the somewhat larger teeth in the males.[156]

Notwithstanding the just discussed slight sex difference in the Eskimo, the facial angle, i. e., the angle between the basi-alveolar line and the line nasion-alveolar point, is equal in the two sexes. This equalization is due largely, if not wholly, to the effect in the males of the relatively longer basio-nasion diameter (v. a.), while the alveolar angle, or that between the basi-alveolar and the subnasal lines, is in general by about 1 per cent lower in the females (males, 56°; females, 55°), indicating a slightly greater slant of the subnasal region in the female, which can only be due to a relatively slightly shorter in this sex of the basion-subnasal point diameter. As a matter of fact, the percentage relation of this diameter to the length of the skull amounts in the males to 56.3, in the females to but 55.6.

Compared to that in the Indians, the facial angle in the Eskimo skulls shows close affinities. Its value (69°) is very nearly the same as in the mound skulls from Arkansas and Louisiana (males 70.7°, females 69°). In other Indians it ranges from close to 68° to 71.5°. In the Munsee it reached 73.5°. In whites, according to Rivet's data,[157] it ranges from about 72° to 75°; in a group of negroes it was 68.5°. In American and other negro crania measured by me[158] it ranged from 67° to 70.5°, in Melanesians from 66° to 68°, in Australians from 67° to 69°.

The alveolar angle is more variable. It shows considerable individual, sex, and group differences. It averages slightly to moderately higher, which means a more open angle or less slant in the males than in the females. In the Eskimo as a whole it was seen to be approximately 56° in the males, 55° in the females; in the Munsee Indians (Bull. 62, Bur. Amer. Ethn.) it was males 59°, females 57°; in the Arkansas and Louisiana skulls (J. Ac. Sci., Phila., 1909, XIV) it averaged males 55°, females 52°. In my catalogue material it shows a group variation of 46.5° to 55.5° in the negro, 47.5° to 52.5° in the Australians, 46.5° to 50.5° in the Melanesians. In the whites it generally exceeds 60°.

Differences in facial and alveolar protrusion among the Eskimo according to area are small, yet they are not wholly absent. The figures below show that in the southwesterners and midwesterners, where the skull is more rounded, the prognathism is smallest; and that toward the north and northeast, where the skull is narrower and the palate (dental arch) tends to become longer, prognathism increases. The "Old Igloo" group shows once more such affinity with the Greenlanders that it is placed with the third subdivision.

Individual group differences in the facial and alveolar angle are moderate, yet evidently not negligible. (See next table.) The most prognathic, especially in the subnasal region, are the skulls from Nelson Island. A marked alveolar slant is also present in the Pilot Station Yukon group, and in Greenland. The least prognathic are the St. Michael Islanders, the Point Hope people, and those from Southampton Island. St. Lawrence stands once more near the middle of the southwesterners and midwesterners, and there are to be seen the principal old relations.

The main points shown by the above conditions are the group variability, particularly in the southwest and midwest; the tendency, on the whole, toward a slightly greater prognathy, both facial and alveolar, in this same area; and the evidence that the alveolar slant has some individuality.