_Anchitherium_, from the Upper Miocene, is not far removed in structure from the last-mentioned form; it is a trifle nearer the existing Horse in several points. The ulna is further reduced and fused with the radius below: the rudiment of digit V is still more rudimentary; the two lateral digits are smaller in proportion to the central one than they are in _Mesohippus_; the fibula is fused below with the tibia. From this form to _Equus_ is a small series of steps, characterised by the still further reduction of all the digits except III, by the still further reduction of the already rudimentary ulna and fibula, and by the increasing depth of the molar teeth, which are of course, in _Equus_, hypselodont. Another interesting conclusion may seem to follow when we consider the geographical range of the ancestral Horses. _Hyracotherium_ and _Pachynolophus_ occurred both in the Old and New World. From them may have arisen the Horses of both hemispheres. After that point there is a division. _Mesohippus_ is American, and we get at _Equus_ in that continent through _Desmatippus_ and _Protohippus_. On the other hand there are no remains known of _Mesohippus_ in Europe; and unless subsequent researches prove the existence of _Mesohippus_, we have to rely upon forms which are placed with _Anchitherium_ and _Hipparion_. It seems that in America the next genus in the direct line of equine descent to _Mesohippus_ is _Miohippus_. It is smaller in {249} size than _Anchitherium_, to be considered immediately. The odontoid process of the axis is just beginning to assume the characteristic spout-like shape of that of the existing Horse and many modern Ungulates. The median digit of both fore- and hind-limbs has become greatly enlarged as compared with the corresponding digit of earlier forms. It is held, however, that _Anchitherium_ is not on the direct line of descent either in America or in Europe, in both of which it occurs. Its teeth are in some respects less Horse-like than in some of the more ancient genera, to which the converse would be expected on the descent theory. Its hoofs are much elongated and flattened, a mark of specialisation and not appropriate to a creature holding an intermediate position in the equine series. Both the American (_A. equinum_) and the European species (_A. aureliense_) are of very large size, larger than its successors, and such "alternations in bulk are unlikely."