PROFESSOR HUXLEY'S LECTURES. 291 



ruals in which the teeth gradually lose the complications of their 

 crowns and have a simpler and shorter crown, while at the same time 

 they gradually increase in size from the anterior end of the series 

 toward the posterior. Let us turn to the facts and see how they bear 

 upon the requirements of this doctrine of evolution. 



In what is called here the Pliocene formation, that which consti- 

 tutes almost the uppermost division of the tertiary series, we find the 

 remains of horses. We also find in Europe abundant remains of horses 

 in the most superficial of all these formations that is, the post-ter- 

 tiary, which immediately lies above the Pliocene. But these horses, 

 which are abundant in the cave-deposits and in the gravels of Eng- 

 land and Europe these horses, of which we know the anatomical 

 structure to perfection are in all essential respects like existing horses. 

 And that is true of all the horses of the latter part of the Pliocene 

 epoch. But in the earlier Pliocene and later Miocene epoch, in depos- 

 its which belong to that age, and which occur in Germany and in 

 Greece, in India, in Bi'itain, and in France, we find animals which are 

 like horses in all the essential particulars which I have just described, 

 and the general character of which is so entirely like that of the horse 

 that you may follow descriptions given in works upon the anatomy of 

 the horse upon the skeletons of these animals. But they differ in 

 some important particulars. There is a difference in the structure of 

 the fore and hind limb, and that difference consists in this, that the 

 bones which are here represented by two splints, imperfect below, are 

 as long as the middle metacarpal bone, and that attached to the ex- 

 tremity of each is a small toe with its three joints of the same general 

 character as the middle toe, only very much smaller, and so disposed 

 that they could have had but very little functional importance, and 

 that they must have been rather of the nature of the dew-claws such 

 as are to be found in many ruminant animals. This Hipparion, or 

 European three-toed horse, in fact presents a foot similar to that which 

 you see here represented, except that in the European. Hipparion 

 these smaller fingers are farther back, and these lateral toes are of 

 smaller proportional size. 



But nevertheless we have here a horse in which the lateral toes, 

 almost abortive in the existing horse, are fully developed. On care- 

 ful investigation you find in these animals that also in the foredimb 

 the ulna is very thin, yet is traceable down to the extremity. In the 

 hind-limb you find that the fibula is pretty much as in the existing 

 horse. That is the kind of equine animal which you meet with in 

 these older Pliocene and later Miocene formations, in which the mod- 

 ern horse is no longer met with. So you see that the Hipparion is 

 the form that immediately preceded the horse. Now let us go a step 

 farther back to the middle and older parts of which are called the 

 Miocene formation. There you find in some parts of Europe the 

 equine animals which differ essentially from the modern horse, though 



