2 9 2 THE POPULAR SCIENCE MONTHLY. 



they resemble the horse in the broad features of their organization. 

 They differ in the characters of their fore and hind limbs, and present 

 important features of difference in the teeth. The forms to which I 

 now refer are what constitute the genus Anchitherium. We have 

 three complete toes ; the middle toe is smaller in proportion, the inner 

 and outer toes are larger, and in fact large enough to rest upon the 

 ground, and to have functional importance not an animal with two 

 dew-claws, but an animal with three functional toes. And in the fore- 

 arm you find the ulna a very distinct bone, quite readily distinguisha- 

 ble in its whole length from the radius, but still pretty closely united 

 with it. In the hind-limb you also meet with three functional toes. 

 The structure of the hind-foot corresponds with that of the fore-foot; 

 but in the hind-leg the fibula is better developed. In some cases I 

 have reason to think that it is complete ; at any rate this lower end 

 of it is quite distinctly recognizable. But the most curious change 

 is that which is to be found in the character of the teeth. The teeth 

 of the Anchitherium have, in the first place, so far as the incisors are 

 concerned, a rudimentary pit. The canine teeth are present in both 

 sexes. The molars are short; there is no cement, and the pattern is 

 somewhat like this (drawing on the blackboard). In the upper jaw, 

 there are two crescents and two oblique ridges, while in the lower 

 jaw you have the double crescent. It is quite obvious that this (illus- 

 trating from drawing) is a simpler form than that. By increasing the 

 complexity of those teeth there, we have the horse's teeth. These are 

 all the forms with which we are acquainted respecting the past his- 

 tory of the horse in Europe. When I happened to occupy myself 

 with this subject some years ago, notwithstanding certain difficulties, 

 the facts left no doubt whatever in my mind that we had here a gen- 

 eral record of the history of the evolution of the horse. You must 

 understand that every one of these forms has undoubtedly become 

 modified into various species, and we cannot be absolutely certain 

 that we have found those species which constitute the exact line of 

 mollification, but it was perfectly obvious that we had here in suc- 

 cession, in time, three forms of the horse-type, of which the oldest 

 came nearest to the general mammal. We saw that the forms which 

 had existed afterward had undergone a reduction of the number of 

 their toes, a reduction of the fibula, a more complete coalescence of 

 the ulna with the radius. The pattern of the molar teeth had become 

 more complicated and the interspaces of their ridges had become filled 

 with cement. In this succession of forms you have exactly that which 

 the hypothesis of evolution demands. The history corresponds ex- 

 actly with that which you would construct a priori from the princi- 

 ples of evolution. An alternative hypothesis is hardly conceivable, 

 but the only one that could be framed would be this, that the Anchi- 

 therium. the Hipparion, and the horse, had been created separately 

 and at separate epochs of time. For that hypothesis there could be 



