EOHIPPUS, the "four-toed horse," the earliest known stage in the ancestry of the horse, found in the Lower Eocene forma tions of the western United States. A number of skeletons and many skulls, jaws or other fragmentary specimens are preserved in American museums. The closely-related Hyracotherium of western Europe is known from a skull and a number of jaws. The species range from the size of a fox to that of a cat. The fore foot has four well-developed toes, the hind foot three, with tiny splints representing the first and fifth digits; the third digit in manus and pes is only slightly larger than the others. The radius and ulna are complete and separate, also the tibia and fibula. The incisors are small, spatulate ; canines larger, pointed ; molars with low rounded cusps partly converted into crests; premolars smaller and simpler than molars. The animal appears to have been digiti grade, walking upright upon the padded toes like the dog or cat, not resting only upon the hoof as do later modern horses. The progressive changes from Eohippus to the existing horses are shown in a series of intermediate stages in the American Tertiary formations (see EQvrDAE).