Forefoot, Neohipparion, ¼ nat. size.

Fig. 11b.—Engraving of a small-headed horse.

PLATE V.

Fig. 12.—Restoration of Eohippus, the American Hyracotherium, size about 12 inches. See fig. 10.

Fig. 13.—Orohippus, a late Eocene four-toed horse, size about 16 inches. See fig. 11.

Fig. 14.—Mesohippus, an Oligocene horse about 24 inches. In some of the three-toed Oligocene horses the cannon-bones were as long as in a 32-inch Shetland pony. See fig 18.

Fig. 15.—Hypohippus, a three-toed Miocene “forest” horse, with the II. and IV. toes long and functional. In 40-inch specimens of Hypohippus the cannon-bones were 2·5 inches longer than in some 40-inch Shetland ponies. See figs. 9 and 20.

Fig. 16.—Merychippus, a 9-hands three-toed Miocene horse. Protohippus (a possible ancestor of modern fine-limbed breeds) and the extinct Hipparions seem to have been derived from Merychippus.

Fig. 17.—A 33-inch Shetland pony. In modern Shelties the legs are relatively shorter than in the three-toed horses of the later Miocene deposits. Shetland ponies have probably partly sprung from ancestors allied to Merychippus and partly from ancestors with limbs of the Hypohippus type.

Figs. 12 to 16 after Osborn and Lull.