The skull carried three pairs of bony protuberances, or horn-like outgrowths; one pair on the nasal bones suggest by their shape and character that they formed the support of dermal horns like those of the paired-horn rhinoceroses (_†Diceratherium_) of the Oligocene and lower Miocene. (See p. 239.) The second pair, which were moderately high and thick prominences, almost cylindrical in shape and tapering but slightly to their bluntly rounded ends, were chiefly outgrowths of the maxillaries, or upper jaw-bones. From their shape, it is likely that these were not sheathed in horn, but were merely covered with skin, as were also the third pair, which arose from the parietals. These were massive, club-shaped prominences, eight or ten inches high and broadening to the free ends, a shape which makes it impossible to suppose that these were true horn-cores covered with horny sheaths. A high crest of bone, representing the occipital crest, enclosed the top and back of the cranium, connecting the posterior pair of “horns” and dying away in front of them. The top of the cranium had thus a deep, basin-like character, such as is to be found in no mammal outside of this suborder and was one of the most peculiar features of this extraordinary skull. The brain-cavity was absurdly small, the growth of the brain not having kept pace with that of the body; the cavity is hidden away in the postero-inferior portion of the skull, the immense thickness of the cranial walls being somewhat lightened by the formation of sinuses, but these were much less extensive and pervasive than in other very large, horned or tusk-bearing mammals, such as elephants, rhinoceroses, etc. Probably, as in the case of the †titanotheres and †entelodonts, this deficiency of brain-development was at least one of the factors which led to the early extinction of the group. The premaxillaries were slender and rod-like bones, which did not meet in the middle line and carried no teeth. The long and massive nasal bones and the position of the nasal opening show that these animals cannot have had a proboscis of any kind. The lower jaw was remarkable for the great bony flange which, in the males, descended on each side from the lower border, near the anterior end, and served to protect the great canine tusks from fracture. [Illustration: FIG. 230.—Skull of †uintathere (_†Uintatherium alticeps_), lower jaw supplied from another species. Princeton University Museum. For restoration, see Fig. 231, p. 447.] The female skull differed in two respects from that of the male: (1) the horn-like protuberances were much more slender and less prominent; (2) as the upper canine did not form a tusk, the lower jaw had no flanges. The skull of the artiodactyl _†Protoceras_ (p. 406) was remarkably similar to that of the †uintatheres.