Now that all the details of the human organisation have been studied, and the anatomical structures of man and large monkeys without tails have been compared, bone with bone and muscle with muscle, a truly astonishing analogy between these organisms is made manifest, an analogy apparent in every detail. It is known that in the natural history of mammals the teeth play an important part as a means of determining differences and relationships. The dentition of man bears a very great resemblance to that of anthropoids. Every one knows the _milk teeth_ and the _permanent teeth_ of man. The anthropoid apes bear in this respect an astonishing likeness to man. The number (thirty-two in the adult), the form and general arrangement of the crown, are identical in man and anthropoid apes. The differences are to be found only in minor details, such as the exact shape and relative dimensions and the number of cusps. It can be said in a general way that in the anthropoid apes the teeth are more strongly developed than in man. The canines are much longer and the roots of the pre-molars are more complex in the gorilla than in man. But the fact must not be lost sight of, that all these differences are less pronounced than those which exist between the dentition of anthropoid apes and that of all other monkeys. Even in the cynocephalous monkeys, those that most nearly approach the anthropoids, the teeth exhibit marked differences. Thus, the forms of the upper molars are quite different in the baboon and in the gorilla. The canines are longer, and the pre-molars and molars are still more complex in the baboon. In the monkeys of the New World, the dentition differs still more from that of man and anthropoids. Instead of thirty-two teeth, they possess thirty-six in the adult condition. The number of pre-molars is twelve instead of eight. The general form and the crowns of the molars are very different from those of anthropoid apes. These considerations led Huxley to conclude that “it is obvious that, greatly as the dentition of the highest ape differs from that of man, it differs far more widely from that of the lower and lowest apes.”[50] Another character which shows that anthropoids are nearer man than other monkeys is furnished by the anatomy of the sacrum. In monkeys as a whole the sacrum is composed of three, or rarely four, vertebræ, while in anthropoid apes it contains five, that is to say just as many as in man. The whole skeleton, and particularly the skull of man, and the higher monkeys, present certainly some marked differences; but here again the differences are less than those between the anthropoid apes and other monkeys. As regards the osteology the proposition laid down by Huxley is just. “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 some other apes.”[51]