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Show 80 very widely from the Gorilla and, in the same way, as Man does; while the Baboons ( Cynocepltalus, Fig. 17) exaggerate the gross proportions of the muzzle of the great Anthropoid, so that its visage looks mild and hun1an by comparison with theirs. The difference between the Gorilla and the Baboon is even greater than it appears at first sight; for the great facial mass of the former is largely due to a downward development of the jaws; an essentially human character, superadded upon that almost purely forward, essentially brutal, development of the same parts which characterizes the Baboon, and yet more remarkably distinguishes the Lemur. Similarly, the occipital foramen of Mycetes (Fig. 17), and still more of the Lemurs, is situated completely in the posterior face of the skull, or as much further back than that of the Gorilla, as that of the Gorilla is further back than that of Man; while, as if to render patent the futility of the attempt to base any broad classificatory distinction on such a character, the same group of Platyrhine, or American monkeys, to which the Mycetes belongs, contains the Clzrysothrix, whose occipital foramen is situated far more forward than in any other ape, and nearly approaches the position it holds in Man. Again, the Orang's skull is as devoid of excessively developed supraciliary prominences as a Man's, though some varieties exhibit great crests elsewhere (seep. 41); and in some of the Cebine apes and in the Chrysothrix, the cranium is as smooth and rounded as that of J\1an himself. What is true of these leading characteristics of the skull, holds good, as may be imagined, of all minor features; so that for every constant difference between the Gorilla's skull proportions of the facial bones. The line b indicates the plane of the tentorium, which separates the cerebrum from the cerebellum ; d, the axis of the occipital outlet of the skull. The extent of cerebral cavity behind c, which is a perpendicular erected on b at the point where the tentorium is attached posteriorly, indicates the degree to which the cerebrum overlaps the cerebellum-the space occupied by which is roughly indicated by the dark shading. In comparing these diagrams, it must be recollected, that figures on so small a scale as these simply exemplify tho statements in the text, the proof of which is to be found in the objects thcrnsch·cs. 81 nnu the Man's, a similar constant difference of the same order (that is to say, consisting in excess or defect of the same quality) may be found between the Gorilla's skull and that of some other ape. So that, for the skull, no less than for the skeleton in general, the proposition holds good, that the differences between Man and the Gorilla are of smaller value than those between the Gorilla and son1e other Apes. In connection with the skull, I may speak of the teeth -organs which have a peculiar classificatory value, and whose resemblances and differences of number, form, and succession, taken as a whole, are usually regarded as more trustworthy indicators of affinity than any others. Man is provided with two sets of teeth-milk teeth and permanent teeth. The former consist of four incisors, or cutting teeth; two canines, or eye-teeth; and four molars} or grinders, in each jaw, making twenty in all. The latter (Fig. 18) comprise four incisors, two canines, four small grinders, called premolars or false molars, and six large grinders, or true molars in each jaw·-making thirty-two in all. The internal incisors are larger than the external pair, in the upper jaw, smaller than the external pair, in the lower jaw. The .crowns of the upper molars exhibit four cusps, or blunt-pointed elevations, and a ridge crosses the crown obliquely, from the inner, anterior, cusp to the outer, posterior cusp (Fig. 18m2 ). The anterior lower molars have five cusps, three external and two internal. The premolars have two cusps, one internal and one external, of which the outer is the higher. In all these respects the dentition of the Gorilla may be described in the same terms as that of J\{an; but in other matters it exhibits many and important differences (Fig. 18). Thus the teeth of man constitute a regular and even series-without any break and without any marked projection of one tooth above the level of the rest; a peculiarity which, as Cuvier long ago showed, is shared by no otl1er G |
