The genus further agrees with the Artiodactyles in the structure of the carpus. The toes of the fore-limb are four, those of the hind-limb three; but while the hind-limb is undoubtedly Perissodactyle in the arrangement of its component parts, the fore-limb shows a hint of an Artiodactyle mode of structure. This limb is paraxonic, the axis of the limb passing between the two middle digits. It may be that this genus represents more nearly than any other Perissodactyle or Artiodactyle the primitive stem from which both have diverged, though, of course, it is not old enough to be very near to the actual ancestor. The molar dentition is the typical one; the incisors seem to vary as to their presence or absence, and, if present, in their numbers. In comparing the older with the more recent forms it is noteworthy that there has been an increase of size exactly as there has been during the evolution of the Camels and some other groups of Ungulates. As already mentioned, the size of the horn cores also increases until it culminates in the extraordinary species, _T. platyceras_ and _T. ramosum_, in which these are half as long as the skull, flattened in form, and connected at their bases by a "web" of bone. Arrived at this amount of specialisation the genus _Titanotherium_ apparently exhausted its capacities for modification and ceased to be. The many generic names may be explained by sexual differences on the one hand and an incomplete knowledge of connecting links on the other.[175] _Palaeosyops_ is somewhat like a Tapir in build, the skull especially resembling that of the Tapir. As in _Titanotherium_ the molar teeth, instead of having an outer wall formed by fused cusps, have a [176]-shaped outer wall on one side and two or one cusps on the opposite side. It is, moreover, an Eocene form, and in correspondence with its greater age is more primitive in some points of structure, for example, in the absence of horns and in the full dental formula. The fore-limbs are four-toed, the hind {267} three-toed. It was intermediate between a Tapir and a Rhinoceros in size. It has been shown, too, from casts of the interior of the skull, that the cerebral hemispheres are much less convoluted than were those of _Titanotherium_.