Fig. 18.—Skeleton of fore-foot of Mesohippus. The II., III., and IV. digits are complete, the V. is represented by the upper end of the metacarpal. Oligocene of America. After Marsh.
Fig. 19.—Forefoot of Merychippus (or Protohippus). Digits II. and IV. shorter than in fig. 18, and the vestige of digit V. very small or absent. American Miocene. After specimen in American Museum of Natural History.
Fig. 20.—Forefoot of Hypohippus, the Miocene “forest” horse. Digits II. and IV. long as in Mesohippus, digits I. and IV. represented by small “splints” not seen in figure. After specimen in American Museum of Natural History.
Fig. 21.—Upper molar, E. stenonis, natural size. The internal pillar (p) is only one-third the length of the grinding surface of the crown. Pliocene. After Boule.
Fig. 22.—Upper molar, E. fossilis, natural size. The internal pillar (p) is more than half the length of the grinding surface of crown. Pleistocene. Kent’s Cavern, Devonshire. After Owen.
Fig. 23.—Premolar and molars (natural size) of a small mediæval? horse from Aberdour, Aberdeenshire. The internal pillars are short. Small horses with short-pillared teeth have lived in Europe since the end of the Pliocene. In the 36·5-inch Shetland pony Eric the molars very closely agree with those figured. From specimens received from Prof. Arthur Thomson, Aberdeen.
Fig. 24.—Premolar and molars of a small horse from the Roman Fort, Newstead. The pillars are long, as in E. robustus of Solutrè and other small Pleistocene horses of Europe; as in the 11-hands E. tau of the Mexican Pleistocene; and as in Shetland ponies of the “forest” or Londonderry type.
Plate VI.