Firstly, there is the true horse. Next we have the American Pliocene form, _Pliohippus_. In the conformation of its limbs it presents some very slight deviations from the ordinary horse. Then comes _Protohippus_, which represents the European _Hipparion_, having one large digit and two small ones on each foot.... But it is more valuable than _Hipparion_, for certain peculiarities tend to show that the latter is rather a member of a collateral branch, than a form in the direct line of succession. Next, in the backward order in time, is the _Miohippus_, [_Miocene_], which corresponds pretty nearly with the _Anchitherium_ of Europe. It presents three complete toes--one large median and two smaller lateral ones; and there is a rudiment of that digit which answers to the little finger of the human hand. The European record stops here: in the American Tertiaries, the series of ancestral equine forms is continued into the Eocene. An older Miocene form, _Mesohippus_, has three toes in front, with a large splint-like rudiment representing the little finger, and three toes behind. The _radius_ and _ulna_, _tibia_ and _fibula_,[278] are distinct. Most important of all is the _Orohippus_, from the Eocene. Here we find four complete toes on the front limb, three toes on the hind-limb, a well developed _ulna_, a well developed _fibula_. Here, when the lecture which we are considering was delivered, the series terminated:--and upon the facts as above given Professor Huxley thus commented: Thus, it has become evident that, so far as our present knowledge extends, the history of the horse-type is exactly and precisely that which could have been predicted from a knowledge of the principles of Evolution. And the knowledge we now possess justifies us completely in the anticipation, that when the still lower Eocene deposits, and those which belong to the Cretaceous Epoch have yielded up their remains, we shall find, first, a form with four complete toes and a rudiment of the innermost or first digit in front, with probably a rudiment of the fifth digit in the hind foot; while, in still older forms, the series of the digits will be more and more complete, until we come to the five-toed animals, in which, if the doctrine of Evolution is well founded, the whole series must have taken its origin. Finally he was able to add in a note that since the delivery of the lecture, Professor Marsh had discovered a new genus of Equine Mammals, _Eohippus_, corresponding very nearly to his description of what might first be looked for. "This," adds Professor Huxley, "is what I mean by demonstrative evidence of Evolution.... In fact, the whole evidence is in favour of Evolution, and there is none against it." * * * * *