North America during Eocene times “was clad with forests in which grew both evergreen and deciduous trees distinctly modern in character. The moist climate gave rise to many streams and lakes, along the shores of which grew sedgy meadows that in turn gave rise to grassy plains.”[F11] In the following (Oligocene) period similar conditions for a time prevailed, but later, owing to the increasing aridity, broad meadow-lands and prairies made their appearance. The new environment produced larger and more active flesh-eaters, fleeter and more intelligent horses. One of the new and improved species is _Mesohippus bairdi_, an 18-inch horse with only a splint-like metacarpal representing the outer or fifth digit—a digit complete in all the Eocene horses. In this as in all the other Oligocene horses three of the four premolars, as in the recent Equidæ, resembled molars. Small and slender-limbed, _Mesohippus bairdi_ was adapted for living in the open, but a larger species (_Mesohippus intermedius_) might be described as a “forest” horse,—though only 24 inches high, this forest-dwelling form had as long cannon-bones as a 33-inch Shetland pony of the “forest” or cart-horse type. Another American Oligocene type (_Miohippus_) from Oregon deserves mention, not so much because it was more specialised, but because it had a representative (probably a descendant) in Europe known as _Anchitherium_, which in Miocene times ranged from France to Bavaria. In this European species the last vestiges of the first and fifth digits had apparently disappeared. The fore limb of _Mesohippus_ is represented in fig. 18, and a restoration is given in fig. 14. It is impossible to say how many thousands of years are represented by the Eocene and Oligocene deposits, but an idea of the time that has elapsed since the beginning of the Tertiary period will be gained if it is mentioned that “when the fox-like _Hyracotherium_ was wandering on the marshes of Kent not only was the Himalaya non-existent, but that along the line of its very heart—where the kiang now lives at an elevation of from thirteen thousand to sixteen thousand feet—extended an arm of the sea of no inconsiderable depth.”[F12] [F12] Lydekker, ‘The Horse and its Relations,’ p. 242.