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 merely selected cases, which do not indicate a wide applicability of such a generalisation. Thus it is true that the brain of a Man is more elaborate in its furrows and convolutions than is that of a Cat. The real fact of the matter is, that the complexity of the brain from this point of view increases with the size of the animal within the group.



The Gorilla and the Chimpanzee have a more furrowed brain than has the little Marmoset; the Bear a more complicated brain than the Weasel, etc. The most highly-convoluted brains of all mammals are those of the Elephants, and there does not seem in the Ungulates to be so marked a relation between size and abundance of fissures as there is among other mammals. A regular plan of the fissures can be detected with certainty for each group considered by itself; but it is not so easy to homologise the details of arrangement from group to group. This is so far in accord with the view that the existing groups of mammals have diverged from each other ab initio.

Another marked characteristic of the mammalian as opposed to other brains is the relatively small importance in size and yet the fourfold nature of the optic lobes. What was the case with the optic lobes of the early Ungulates is difficult to understand, on account of the fact that the casts are necessarily imperfect.