The same disproportion in the size of the more ancient animal's brain is found when we compare the brain of the modern horse with that of its early tertiary ancestors. The modern animal has, as a rule, a very greatly increased size of brain when compared with its Miocene forefather. In fact, it seems that the brain has had, as it were, an independent development in several lines of descent, and whilst the rest of the structure of the ancestral form has been only slightly modified in its proportions, the brain cavity and the brain within it has enormously increased. It is therefore not so exceptional a thing as it at first appears--but only an instance of a change more or less widely exhibited among later animals, as compared with their near relatives in the past--when we establish the fact that the brain of the man-like apes is much bigger than that of lower monkeys, and that the brain of man, who is so closely similar in all structural details to those apes, has attained to a bulk three times that of the ape. The vast increase in the size of the brain in recent animals, as compared with their closely related representatives of an earlier period, is a frequent and regular thing. It is possible to make a suggestion, of some plausibility, as to the meaning and value of this increased size of brain, which will be found in the next chapter. CHAPTER XXIX THE MIND OF APES AND OF MAN JUST as man's brain is enormously larger than that of the ordinary monkeys, although his general make and anatomy is closely similar to theirs, so we find that the rhinoceros has an enormous brain as compared with extinct rhinoceros-like animals, the predecessors and ancestors of those now living. The extinct Titanotherium of the lower Miocene period managed to carry on its life in an efficient way and to hold its own for a considerable period with a brain which was only one-eighth the bulk of that of a modern rhinoceros, as did other animals in the past with even greater bodies and smaller brains. To get some suggestion as to the significance of this fact we must, in however incomplete a way, distinguish some of the main features of the mental processes which go on in man and animals and have their "seat" in the brain.