ciens) which, in their turn, are similarly superior to the rest There is an almost continuos series of modifications, of degradations, which are the more diverse, as they are far from always affecting to a similar degree the development of the anterior lobe, and that of the corpus callosum, or the condition of the convolutions. It may and does happen, that these remain very numerous in a cerebum with its anterior lobes and corpus callosum more or less reduced; or, on the other hand, they may be more or less obsolete in a brain which is still remarkable for its general development, for the extent of its corpus callosum, and the volume of its anterior lobes. This last combination is that presented by many apes of the third tribe (Cebiens), especially, and more than by any other genus of the same group, by the Saimiris, which are so remarkable for the richness of their cerebral development. The same combination is found, but carried to a still greater excess, in all the apes of the fourth tribe (Hapaliens). In the Marmosets the brain is, at the same time, greatly developed as a whole (less however than in the Saimiris) and is devoid of convolutions; it is one of the richest brains in one direction, one of the poorest in the other.
"These facts have not yet been reduced to a law, either for the whole brain, or for the corpus callosum, or for the anterior lobes; but their connexion is easily apprehended, so far as the convolutions are concerned. If for the too complex comparison of generic differences, we substitute that of the general differences between one tribe and another, the following is the immediate result:—In Man, the convolutions are very numerous and are separated by deep sulci; in the first tribe (Simiens) they are less numerous than in Man, more numerous than in the second; in the second tribe (Cynopitheciens) they are more numerous than in the third (Cebiens); in which the cerebral gyri become more and more scanty, from Atelas and the Cobi to the Saimiris and the Callitriches; exhibiting a gradual progress towards the fourth tribe (Hapaliens) which is distinctly characterized by the smoothness of the brain.
"There is, then, a decrease in the convolutions in a serial order, from Man to the first, second, third, and fourth tribes; which in this point of view constitute five terms of one and the same very regular series, from the maximum of the development of the convolutions observed in Man, to their complete disappearance in the Marmosets—and this series ends at the exact point, where the family of the Lemuridæ succeeds to that of the Apes; a distinct series in which we see (in a brain in other respects very differently constructed), the convolutions re-appear at the upper end of the scale, in the Indri and the Lemurs, to disappear anew, at the lower end, in Microcebus.
"Whence flows this consequence, that may and will be better defined, but will not be rendered more certain by future investigations: In any classification based on the constitution of the brain and particularly on the condition of the convolutions, two general divisions must be established among the Primates, one for man and all the apes, the other for the Lemuridæ; and in the former two sub-divisions: man and the apes with convolutions; then the apes with smooth brains.
"In other words, man is, in this respect, much nearer the higher Apes, than these are, not merely to the Lemurs, but even to the lower types of their own family."After this dear and, upon the whole, just statement of the cerebral relations of man to the apes, M. St. Hilaire takes up the question of the facial angle. This angle, measured by the method of Geoffroy and Cuvier, he affirms to become as small as 64° in a South African people, the Makoias; which is 6° less than the limit ordinarily assigned to it in the human species. But in the adult Saimiri the facial angle measured in the same way amounts, he affirms, to 65°, and is but a few degrees less in the Gibbons and the Semnopitheci, among the old world apes; in Cobus, Ateles, Eriodes, Lagothrix, Callithrix and Nyctipithecus among the apes of the new world. After which, says M. St. Hilaire:—
