The lower jaw of the Eskimo deserves a thorough separate study. For this purpose, however, more jaws in good condition are needed from various localities, and particularly more jaws accompanying their skulls. As it is, a large majority of the crania are without the lower jaw, or the alveolar processes of the latter have become so affected in life through age and loss of teeth that their value is diminished or lost. Still another serious difficulty is that the measuring of the lower jaw is difficult and has not as yet been regulated by general agreement, so that there is much individualism of procedures with limited possibilities of comparison.

One of the principal measurements taken on the available Eskimo mandibles was the symphyseal height. This is taken by the sliding calipers and is the height from the lower alveolar point (highest point of the normal alveolar septum between the middle lower incisors) to the lowest point on the inferior border of the chin in the median line.[161] The results are given in the following tables.

Just what these figures mean will best be shown by a table of comparisons.[162] All these are my own measurements.

The table shows the Eskimo jaw to be absolutely the highest at the symphysis of all those available for comparison, with the female nearly the highest.[164] Relatively to stature it exceeds decidedly all the groups, the Indians that come nearest matching it in the absolute measurement being all much taller than the Eskimo. And the female Eskimo jaw is relatively high compared with that of the male, being exceeded in this respect only in three of the Indian groups, in two of which, however, the showing is due wholly and in one partly to a lesser height of the male jaw. The relative excess of the female jaw in this respect seems particularly marked in the northern and northeastern groups, though it must remain subject to corroboration by further material.

The white, Negro, and Australian data have an interest of their own.

Strength of the Jaw

The Eskimo jaw is generally stout. Barring rare exceptions there is nothing slender about it. The body, moreover, is frequently strengthened by more or less marked overgrowths of bone lingually below the alveoli and above the mylohyoid ridge. These neoformations will be discussed later.

The strength of the mandible may be measured directly in various locations on the body. Due to the peculiar build of the body, however, and especially to its variations, these measurements are by no means simple and wholly satisfactory. It is hardly necessary in this connection to review the various attempted methods, none of which has become standardized. As a result of experience I prefer since many years to measure the thickness of the body of the jaw at the second molars, and that in such a way that either the molars, if the measurement is taken from above, or the lower border of the jaw if it is taken from below, lies midway between the two branches of the sliding calipers with which the measurement is taken. The two methods (from above or below) give results that are nearly alike. In some cases the one and in others the other is the easier, but wherever the teeth are lost the measurement from below is perhaps preferable. The records obtained on the lower jaws of the western Eskimo and other racial groups are given in the next table.

The figures show that the Eskimo jaw is very stout. It is exceeded in thickness only by the jaws of Florida, which in general are the thickest in America, and in males is about equaled, in females very slightly exceeded by those of the prehistoric Indians of Louisiana, who belong to the same Gulf type with the Indians of Florida. The old Arkansas Indians, though closely related to those of Louisiana, show a very perceptibly more slender jaw, particularly in the males; while in an old Kentucky tribe (Green River, C. B. Moore, collector) the jaws are still less strong. The lower jaws of the American whites (dissecting-room material) are slightly less stout than even those of the Indians of Kentucky in the males, and much less so in the females. The interesting sex differences are shown well in the last column of the above table.

Breadth of the Rami

Still another character that reflects the strength of the lower jaw is the breadth of the rami. The most practicable measurement of this is the breadth minimum at the constriction of the ascending branches. A great breadth of the rami is very striking, as is well known, in the Heidelberg jaw, and the Eskimo have long been known for a marked tendency in the same direction. The measurements of the lower jaws of the western Eskimo show as follows:

The Eskimo jaws, and particularly that of the female (relatively to other females), have the broadest rami. Otherwise the series range themselves in the same order as under the measurement of the stoutness of the body.

Other Dimensions

Four other measurements were taken on the jaws, namely the length of the body (on each side); the height of the two rami; the bigonial diameter; and the body-ramus angle. The results of the first three may conveniently be grouped into one table.

The Eskimo lower jaw, which, as seen before, is characterized by a high and stout body and the broadest rami, shows further that these rami are remarkably low, and that the bigonial spread is extraordinarily broad. The length of the body, on the other hand, is not very exceptional, being perceptibly exceeded in some of the Indians.

The Angle

The angle between the body and the ramus of the lower jaw is known to differ with the age and sex as well as individually. Not seldom it differs also, and that sometimes quite appreciably, on the two sides. Racial differences are as yet uncertain.

The angle, especially in some specimens, is not easy to measure, and the position of the jaw may make a difference of several degrees. Numerous trials have shown that the proper way is to measure the angle on the two sides separately, and to so place the jaw in each case that there is no interference with the measurement by either the posterior or the anterior enlarged end of the condyle.

Leaving out jaws in which extensive loss of teeth has in all probability resulted in changes in the angle, the western Eskimo material gives the following data:

In the male Munsee Indians the angle was 118°; in those of Arkansas and Louisiana, 118.5°; in those of Peru (Martin, Lehrb., 884), 119°. In the whites, males, the average angle approximates 122°; in the Negro, 121° (Topinard, Martin).

The angle in the female in the Eskimo is to that of the male as 104 to 100; in the Arkansas and Louisiana series it was 103. In the whites the proportion seems to be a little higher.

There are evidently, if we exclude the whites in whom the shortness of the jaw conduces probably to a wider angle, no marked racial differences, but the subject needs a more thorough study on large series of sexually well-identified specimens, carefully selected as to age.

The average angle on the right differs in the Eskimo but very slightly from that on the left, though individually there are frequent unequalities.

RÉsumÉ

The Eskimo lower jaw differs substantially in many respects from that in other races, particularly from that of the whites. It is characterized by a high and stout body; by broad but low rami; and by excessive breadth at the angles. The body-ramus angle is moderate. To which may be added that the chin is generally of but moderate prominence, and that the bone at the angles in males is occasionally markedly everted.

Mandibular Hyperostoses

These hypertrophies or hyperostoses are rarely met with also in the jaws of the Indian and other people. They are symmetric and characteristic, though often more or less irregular. They generally extend from the vicinity of the lateral incisors or the canines backward, forming when more developed a marked bulge on each side opposite the bicuspids, which gives the inner contour of the jaw when looked at from above a peculiar elephantine appearance. They may occur in the form of smooth, oblong, somewhat fusiform swellings, or as a continuous more or less uneven ridge, or may be represented by from one to four or five more or less rounded or flattened hard "buttons" or tumorlike elevations. In development they range from slight to very marked.

These hyperostoses have been reported by various observers (Danielli, SØren Hansen, Rudolf Virchow, Welcker, Duckworth & Pain, Oetteking, Hrdlicka, Hawkes). They received due attention by FÜrst and Hansen in their "Crania Groenlandica" (p. 178). They have been given the convenient, though both etiologically and morphologically inaccurate, name of "mandibular torus"; I think mandibular hyperostoses or simply welts would be better. FÜrst and Hansen found them, taking all grades of development, in 182, or 85 per cent, of 215 lower jaws of Greenland Eskimo; in 28 jaws, or 13 per cent, they were pronounced, the remainder being slight to medium. A special examination of 62 lower jaws of children and 710 lower jaws of adult western Eskimo (with a small number from Greenland) gives the following record:

The significance of these hyperostoses is not yet quite clear. Danielli, who in 1884 reported them[171] in the Ostiaks, Lapps, a Kirghiz, a Peruvian Indian, and four white skulls, offered no explanation. For SØren Hansen,[172] who first suggested the resemblance of these formations to the torus palatinus, "the significance of this feature, which also occurs in other Arctic races not directly related to the Eskimos, is not clear." R. Virchow,[173] who reports "wulstigen und knolligen Hyperostosen" on both the upper and lower jaws of a Vancouver Island Indian, restricts himself to a brief mention of the condition with a suggestion as to its causation (see later). Welcker[174] found them in the skulls of a German (Schiller?), Lett, and a Chinese, but has nothing to say as to their meaning. Duckworth and Pain[175] report the "thickening" in 10 out of 32 Eskimo jaws, but do not discuss the causation; and the same applies to Oetteking,[176] who reported on a series of Eskimo from Labrador. In 1909 Gorjanovic-Kramberger[177] somewhat indirectly notes the condition, without a true appreciation of its meaning.

In 1910 I had the opportunity to report on the mandibular hyperostoses in a rare collection of crania and lower jaws of the central and Smith Sound Eskimo.[178] Of 25 lower jaws of adults and 5 of children, 18, or 72 per cent, of the former and 2 of the latter showed distinct to marked lingual hyperostoses, while in the remaining cases the feature was either doubtful (absorption of the alveolar process) or absent. Two of the five children showed the peculiarity in a well-marked degree. A critical consideration of the condition leads me to the conclusion that it is not pathological, and my remarks were worded (p. 211) as follows: "A marked and general feature is a pronounced bony reinforcement of the alveolar arch extending above the mylohyoid line from the canines or first bicuspids to or near the last molars. This physiological hyperostosis presents more or less irregular surface and is undoubtedly of functional origin, the result of extraordinary pressure along the line of teeth most concerned in chewing; yet its occurrence in infant skulls indicates that at least to some extent the feature is already hereditary in these Eskimo."

In 1912, Kajava[179] reported lingual hyperostotic thickenings on the lower jaws of 68 adult Lapps, and found the condition in frequent association with pronounced wear of the teeth. In 1915, finally, FÜrst and C.C. Hansen, in their great volume on "Crania Groenlandica," approach this question much more thoroughly. They, as also Kajava, did not know of the writer's report of 1910. They found the "torus" (p. 181), "also in the mandibles of some various Siberian races in a not insignificant percentage *** and also not infrequently among European races, especially in the Laplanders (30 to 35 per cent)." They also report the presence of the condition "in a Chinaman," and saw indications of a good development of it in 17 per cent of 164 middle ages to prehistoric, and in 12 per cent of later Scandinavian lower jaws. Their interesting comments on its possible causation, though at one point seemingly not harmonizing, are as follows (p. 180): "The possibility is not precluded that we have here a formation which, even though it has at first arisen and been acquired through mechanical causes, has in the end become a racial character, albeit a variable one." And page 181: "There seems to be no doubt whatever that it is a formation connected with Arctic races or Arctic conditions of life; and, accordingly, it can not safely be assumed to be a racial character, however difficult it is to regard it as a formation only acquired individually."

With both the previously published and the present data, I believe the subject of these bony formations may now be approached with some hope of definite conclusions.

These hyperostoses give no indication of being pathological. They are formed largely, if not entirely, by compact bone tissues of evidently normal construction. They never show a trace of attending inflammation or of ulceration or of breaking down. They resemble occasionally the osteomae of the vault of the skull, and more distantly the osteomae of the auditory meatus, but in those cases where the bony swelling is uniform and in many others they show to be of quite a different category. (Pl. 61.)

As a rule these bony protuberances in the Eskimo are not connected with evidence of pyorrhoea, root abscesses, or any other pathological condition of the teeth, for those conditions are practically absent in the older Eskimo skulls; therefore they can not be ascribed to any irritation due to such conditions, and the Eskimo have no habits that could possibly be imagined as favoring, through mechanical irritation, the development of these bony swellings. Wear of the teeth, which has been thought to stand possibly in a causative relation to these developments, is common in many races and even in animals (primates, etc.), without being accompanied by any such formations.

The development of such overgrowths is not wholly limited, as already indicated from the cases reported by Danielli (1884) and Virchow (1889), to the lower jaw, but somewhat similar growths may also be observed, though much more rarely, both lingually and on the outer border of the alveolar process of the upper jaw in the molar region. When present in the latter position they interfere with the measurement of the external breadth of the dental arch.

But, if neither pathological themselves nor due to any pathological or mechanical irritation, then these hyperostoses can only be, it would seem, of a physiological, ontogenic nature; and if so, then they must be brought about through a definite need and for a definite purpose or function.

These views are supported by their marked symmetry, which is very apparent even where they are irregular; by the fact that in general they are not found in the weakest jaws (weak individuals), or again in the largest and stoutest mandibles (jaws that are strong enough, as it is); and by the history of their development.

Our rather extensive present data on children show that these formations are absent in infancy. They begin to develop in older childhood, in adolescence, or even during the earlier adult life; they stop developing at different stages in different individuals, and they never lead to any deformity of the body of the mandible.

These overgrowths are further seen to be more common and to more frequently reach a pronounced development in the males than in the females.

What is the effect of these hyperostoses? They strengthen the dental arch. With them the arch is stronger; without them it would be weaker. The view is therefore justified that they augment the effectiveness of the dental arch; which is just what is needed or would be useful in such people as the Eskimo where the demands on the jaws exceed in general those in any other people.

All these appear to be facts of incontrovertible nature; but if so then we are led to practically the same conclusion that I have reached in the study of the central and Smith Sound Eskimo, which is that the lingual mandibular hyperostoses are physiological formations, developed in answer to the needs of the alveolar portions of the lower jaw. They could be termed synergetic hyperostoses.

The process of the development of these strengthening deposits of bone is probably still largely individual; yet the tendency toward such developments appears to be already hereditary in the Eskimo, as indicated by their beginning here and there in childhood. But their absence in nearly one-third of the Eskimo mandibles, their marked differences of occurrence and development in the two sexes, and their occasional presence in the jaws of various other peoples, including even the whites, speak against the notion of these hyperostoses being as yet true racial features.

Taking everything into consideration, the writer is more than ever convinced that the lingual hyperostoses of the normal lower (as well as the upper) jaw, in the Eskimo as elsewhere, are physiological, ontogenic developments, whose object and function is the strengthening of the lower alveolar process in its lateral portions. Only when excessively developed, which is very rare, they may, mechanically, perhaps cause discomfort and thereby approach a pathological condition.

Main References

Danielli,[180] 1884: "Saw the condition in lower jaws of 1 Swede, 1 Italian, 1 Terra di Lavoro jaw, 1 Slovene, 1 Hungarian, 1 Kirghis, 1 ancient Peruvian."

Found hyperostoses in 9 out of 14 Ostiak lower jaws.

Material: Young 2, adult 6, old 6.

Hyperostoses in young 1, adult 3, old 5.

Mantegazza, at his request, examined some Ostiak and Eskimo skulls in Berlin and found the hyperostoses in 2 Ostiak lower jaws (slight) and in 1 Eskimo skull from Greenland (marked).

Found also smaller hyperostoses in the upper jaw ventrally to the molars ("situate quasi sempre dalla parte interna in corrispondenza dei molari"):

Skulls: 2 Italians, 1 Hungarian, 7 Norwegians, 2 Lapps, 5 Ostiaks.

Plate shows 8 lower jaws, 1 with slight, 7 with marked hyperostoses (1 symphyseal swellings, 3 tumorlike).

Refrains from interpretation (could not reach conclusion).

Virchow,[181] 1889, page 392: In upper jaws of three Santa Barbara skulls: "An den AlveolarrÄndern der weiblichen SchÄdel Nr. 3-6 von S. Barbara besteht eine hÖchst eigenthÜmliche und seltene, knollige Hyperostosis s. Osteosclerosis alveolaris, wie ich sie in gleicher StÄrke frÜher nur bei Eskimos gesehen hatte. Ein leichter Ansatz dazu zeigt sich auch bei dem mÄnnlichen SchÄdel Nr. 4 von S. Cruz. Es dÜrfte dieser Zustand, der mit tiefer Abnutzung der ZÄhne zusammenfÄlt, durch besonders reizende Nahrung bedingt sein."

Vancouver Island skulls: "dagegen sehen wir dieselbe alveolare Hyperostose, die wir bei den Leuten von S. Barbara und weiterhin bei Eskimos kennen gelernt haben."

Virchow,[182] 1892: "Der Alveolarrand gleichfalls mit hyperostotischen WÜlsten besetzt, jedoch mehr an der inneren Seite, besonders stark in der Gegend per PrÜmolares und Canini, weniger stark in der Gegend der Incisici."

Welcker,[183] 1902: "Exostosen der AlveolarrÄnder. Von erheblicher Beweiskraft kÖnnen EigenthÜmlichkeiten und AbnormitÄten des Knochengewebes under der KnochenoberflÄche werden, wenn dieselben, bei an sich grosser Seltenheit ihres Vorkommens, an einem OberschÄdel und Unterkiefer zugleich vorkommen.

"So fand ich am Unterkiefer der GypsabgÜsse des sogenannten SchillerschÄdels sehr merkwÜrdige, bis dahin nirgends erwÄhnte, erbsenfÖrmige Exostosen an den Alveolen der Eck- und SchneidezÄhne. Ganz Ähnliche, wenn auch etwas flÄchere Exostosen zeigen die Alveolen eben derselben ZÄhne des OberschÄdels, und es beweist dieses seltene Vorkommen bei dem Zutreffen aller Übrigen Zeichen das ZusammengehÖren beider StÜcke mit hoher Sicherheit.

"In einer etwas anderen Form, in der dieselben einen geschlossenen, exostotischen Saum bilden, fand ich Alveolarexostosen bei einem LettenschÄdel (G. Gandras, 47 J., Halle Nr. 52). Hier sind die AlveolarrÄnder der Schneide-und EckzÄhne mit flachen, am Oberkiefer streifenfÖrmigen (senkrecht gestellten), am Unterkiefer mehr rundlichen Exostosen besetzt, so dass der sonst papierdÜnne ZahnflÄchenrand beider Kiefer in einen, die ZahnhÄlse begrenzenden wulst-fÖrmigen Saum umgewandelt ist. Der gleiche Charakter dieser nicht hÄufigen AbnormitÄt an beiden Kiefern giebt die vollste Ueberzeungung der ZusammengehÖrigkeit.

"In schwÄcherem Grade zeigt diesen Zustand ein ChinesenschÄdel der Halle'schen Sammlung (Lie Assie)."

FÜrst,[184] 1908: "Wir haben hier auf diese interessante anatomische Bildung aufmerksam machen wollen, die, wenn nicht konstant, doch in sehr hohem Prozentsatze und in bestimmter charakteristischer Form bei den Eskimos auftritt und in verschiedenen Variationen auf dem Unterkiefer anderer Rassen, speziell nordischer oder arktischer, vorkommt.—Wir wollen spÄter eine ausfÜhrlichere Beschreibung Über den Torus mandibularis mitteilen."

Gorjanovic-Kramberger,[185] 1909: "Durch die Ausbiegung der seitlichen KieferflÄchen wÜrde ferner die Druckrichtung der M und P eine gegen die innere Kieferwandung gerichtete. Als direkte Folge dieses Druckes hat man die starke Ausladung der entsprechenden lingualen Kieferseiten im Bereiche der P und M anzusehen, die da eine auffallende Einengung des inneren Unterkieferraumes bewerkstelligte."

Hrdlicka (A.), 1910. See text.

Hansen,[186] 1914: "The lower jaws attached to the skulls are powerfully formed, high, and, above all, very thick, their inner surface being markedly protruding, rounded, and without any special prominence of linea mylohyoidea. This peculiarity, which is common enough, among the Eskimo and certain Siberian tribes, but is otherwise exceedingly rare, must be regarded as a hyperostosis of the same nature as the so-called torus palatinus. It is a partly pathological formation due to a peculiar mode of life rather than a true morphological mark of race."

FÜrst, C. M., and Hansen, C. C., 1915. See text.

Cameron,[187] 1923: "In some instances the bony thickening was excessive. For example, in mandible XIV H-8 the inward bulging of the bone was so marked that the transverse distance between the inner surfaces of the body opposite the first molars was reduced to 21.5 millimeters. This jaw had therefore an extraordinary appearance when viewed from below. (See fig. 5.) The writer would regard these bulgings as bone buttresses built up by nature to resist the excessive strain thrown upon the alveoli of the molar teeth. He exhibited the mandibles to Prof. H. E. Friesell, dean of the dental faculty, University of Pittsburgh, and this authority concurred in the opinion expressed above." A disagreement with this view is expressed by S. G. Ritchie, pages 64c-65c, same publication.

[180] Danielli, Jacopo, Iperostosi in mandibole umano specialmente di Ostiacchi, ed anche in mascellari superiore. Archivio per l'antropologia e l'etnologia, 1884, XIV, 333-346.