It is surmised by Professor Scott that the number of dorso-lumbar vertebrae was twenty-three or twenty-four. The radius and ulna are complete and separate bones, but the latter is somewhat reduced. There are four metacarpal bones, of which, however, the fifth is much reduced. The animal is only three-fingered. The tibia and the fibula are distinct, and show no tendencies towards fusion; but the fibula is much reduced. There are only three metatarsals and three toes. Had this line, which is to be regarded as a side branch of the Rhinoceros stem, not died out, it would probably have resulted, thinks Professor Scott, in monodactyle--very Horse-like types. It is later than the next genus to be described, _Hyrachyus_, of which it is possibly a descendant. An intermediate type, _Triplopus_, appears to bind together _Hyracodon_ and _Hyrachyus_. In _Hyrachyus agrarius_ the skull is long and narrow, the facial region being markedly longer than in existing Rhinoceroses. The mastoid portion of the periotic bone is widely exposed upon the outer face of the skull, which is, as has been said, not the case with the existing genus _Rhinoceros_. The dentition is the complete Eutherian dentition of forty-four teeth. The upper {263} molar teeth are strikingly like those of the genus _Rhinoceros_. The fore-feet are pentadactyle, but functionally tetradactyle; the hind-feet tridactyle. The ulna is less reduced than in _Hyracodon_, and the dorso-lumbar vertebrae are twenty-five. [Illustration] FIG. 136.--Skeleton of _Metamynodon planifrons_. x 1/22. (After Osborn and Wortman.) The Amynodonts were short, heavy types, probably marsh-haunting in habit, and possibly with a proboscis like that of the Tapir. The orbit is higher than it is in the purely terrestrial {264} Hyracodonts, and it is suggested that when swimming it was raised above the surface as with the Hippopotamus. "This feature," observes Professor Osborn, "with the long curved tusks, undoubtedly used in uprooting, suggests the resemblance between the habits of these animals and those of the hippopotami." There were no horns in the Amynodonts. The face is shorter than in the Hyracodonts, and the mastoid is covered as in recent Rhinoceroses. The canines are very strongly developed into tusks, but the incisors show signs of disappearance. We know of the genera _Amynodon_, _Metamynodon_, and _Cadurcotherium_. All except the last, which is European, are American in range.