In the Middle Eocene, the place of _Coryphodon_ was taken by _Dinoceras_ and allied forms. Some of the species nearly equalled the elephant in size, but had shorter and stouter limbs, each supported on five great toes—the most perfect possible sort of pedestal foot (Figs. 172, 174). They were heavily armed with immense canines on the upper jaws, and two or even three pairs of horns or hard protuberances on the head (Fig. 173). Creatures so supported and so armed, and living where food was plentiful, might well dispense with any great degree of intelligence, and their development of brain is consequently little better than that of _Coryphodon_. These great and characteristic Eocene families have no known successors; and in the Miocene age their place is taken by a very different group, that of which _Brontotherium_ is the type (Fig. 175). They are creatures of huge size, with a pair of horn-cores on the nose, and feet with four toes in front and three behind, resembling in form those of the rhinoceros. [Illustration: FIG. 174.—Fore-foot of _Dinoceras_. Greatly reduced.—After Marsh.] [Illustration: FIG. 175.—Skull of _Brontotherium ingens_ (Marsh). Greatly reduced. A Miocene Perissodactyl.] [Illustration: FIG. 176.—Series of Equine Feet.—After Marsh. _a_, _Orohippus_, Eocene. _b_, _Miohippus_, Miocene. _c_, _Protohippus_, Lower Pliocene. _d_, _Pliohippus_, Upper Pliocene. _e_, _Equus_, Post-Pliocene and Modern.] While these gigantic Perissodactyles have no successors as yet known to us, another and less conspicuous Eocene type can be traced onward to modern times by a chain of successors which the imagination of evolutionists has converted into a veritable genetic series, to which they appeal as a “demonstration” of the process of descent with specific modifications. In the Lower Eocene are found the remains of a diminutive ungulate (_Eohippus_), of the stature of a moderately-sized dog. It has four toes and a rudiment of a fifth in front, and three toes behind; and has teeth slightly resembling those of the horse, but more simple and shorter in the crown. In this creature it has been supposed that we have a direct ancestor of the modern horse. A very similar genus (_Orohippus_), lacking only the fifth rudimentary toe, replaces _Eohippus_ in the Middle Eocene. _Mesohippus_ of the Lower Miocene is as large as a sheep, and has only three toes on the fore-foot and a splint bone, while its teeth assume a more equine character (Fig. 176). In the Upper Miocene _Miohippus_ continues the line, while _Protohippus_ of the Lower Pliocene is still more equine and as large as an ass, and corresponds with the European _Hipparion_ in having the middle toe of each foot alone long enough to reach the ground. In the Upper Pliocene true horses appear with only a single toe, and splint bones instead of the others. In America, though the horse was unknown at the time of the discovery of the continent, several species occur in the Tertiary and