Plate VI.—The series of teeth in the upper (1) and lower jaw (2) of a modern European (natural size). The teeth are placed closely side by side without a gap—an arrangement which does not occur in the apes nor in any other living mammal, although it is found in some extinct herbivores—the Anoplotherium and the Arsinöitherium. The shape of the arch formed by the row of teeth should be compared with that shown by the same arch in the Gibbon (Pl. VII). The crowns of the teeth are very carefully drawn in this figure, which is from a plate published by Professor Selenka.
It must be noted that the number of tubercles on the true molars may be in exceptional cases one more or one less than that given in this drawing which gives the most usual number. The word "molar" is often used to include the five cheek-teeth on each side of each jaw, but more strictly the anterior bicuspid teeth are called "pre-molars," and the three larger teeth behind them, which have no predecessors or representatives in the first or milk dentition, are called true molars or simply "molars"—a rule we have followed here.
In both upper and lower jaw we see the four incisors in the middle (Inc. 1, Inc. 2); on each side of them is the conical crown of a canine—a tooth which is greatly enlarged in the ape (see Pl. VII), but is no larger proportionately than it is here even in the most ancient known human jaw, that from the Pleistocene of Heidelberg (see "Science from an Easy Chair," Methuen, 1910, p. 405). The two small bicuspid "pre-molars" and the three large molars follow these on each side in each jaw. The crown of the most anterior (or "first") molar of the upper jaw has four cusps, tubercles, or cones on it. It is "quadri-tuberculate." The second and third molars of the upper jaw have three such prominent tubercles (excluding a row of small tubercles on the hinder margin of the second); they are, in fact, tri-tuberculate; whilst the two hindermost molars of the lower jaw have four tubercles and are called quadri-tuberculate. The first molar (M1) of the lower jaw has in this specimen five tubercles. In 60 per cent. of European lower jaws this is the case. But in 40 per cent. this tooth is quadri-tuberculate. In Polynesians, Chinese, Melanesians and negroes five tubercles are found on this tooth in 90 per cent. of the jaws examined. The apes are characterised by five tubercles on this tooth, and they are found also on the first lower molars of prehistoric men. Four tubercles only on this tooth is a departure from the ape's condition and is found more frequently in Europeans.
It is obvious that these big molar teeth, as well as the two smaller ones in front of them on each side of each jaw, are adapted for breaking up rather soft, pulpy food, and not for cutting lumps of bone or raw flesh, as are the molars of the clouded tiger (identical with those of all species of the genus Felis), shown in Figs. 21 and 22, pp. 103, 104, nor for rubbing grain, grass or herbage to a paste, as are those of the goat (Fig. 17), those of the Coypu rat (Fig. 19), and those of the elephants and mastodons (Fig. 8).
Plate VII.—Drawings of (1) the upper and (2) the lower series of teeth of the Gibbon (Hylobates concolor), one of the anthropoid or most man-like apes (enlarged by one third). If these drawings are compared with those in Pl. VI, showing man's teeth, the most striking difference seen is that the "arch" or series of teeth is here elongated and squared, not rounded in front, whilst there is plenty of room in both jaws for the last or wisdom tooth, which is not the case in modern races of men, though in the ancient Neander man's jaw and in that from Heidelberg there is ample space for the last molar as in the apes. The next most important difference is that in the gibbon the four canine teeth are very large and tusk-like, and must certainly be of value as weapons of attack—which man's are not. Connected with the large size of the canines is the presence of a gap (or "diastema" as it is called) between the four front teeth or incisors of the upper jaw and the upper canine—which allows the lower canine to fit in front of the upper canine when the jaw is closed. The number of the tubercles or cones on the molars (the two smaller pre-molars and the three hinder large molars) can be compared in detail in these beautiful drawings from Professor Selenka's work, which are the most careful and perfect which have ever been published. The agreement of these teeth in man and the gibbon is very close: but there are differences. The first, or most anterior pre-molar of the lower jaw has one predominant cusp or cone; the second, like both in the upper jaw, is "bicuspid," or bi-tuberculate, as in man. The three big molars of the upper jaw are closely similar to those of man, with some small differences, the second being quadri-tuberculate, whilst in man it is as often tri-tuberculate (as it is in Pl. VI) as it is quadri-tuberculate. But the two anterior big molars of the lower jaw are seen to have each five well-marked cones, cusps or tubercles; they are quinqui-tuberculate, whilst in man the first lower molar is often quadri-tuberculate and the second even more frequently so. The last lower molar (wisdom tooth) of the gibbon is like that of man, quadri-tuberculate.
The details of the tubercles on these molar teeth distinctly justify the conclusion that they are adapted in the two animals compared—namely, man and the gibbon—to food of the same mechanical quality, and this undoubtedly is fruit and nuts. Nevertheless such a form of tooth is equally well adapted to the texture of cooked meat, which has served many races of man for probably hundreds of thousands of years as food.