210 DESIGN IN NATURE 



dew-claws, such as are to be found in many ruminant animals. The Hipparion, as the extinct European three- 

 toed horse is called, in fact, presents a foot similar to that of the American Protohippus, except that, in the 

 Hipparion, the smaller digits are situated further back, and are of smaller proportional size, than in the 

 Protohippus. 



" The ulna is slightly more distinct than in the horse ; and the whole length of it, as a very slender shaft, in- 

 timately united with the radius, is completely traceable. The fibula appears to be in the same condition as in 

 the horse. The teeth of the Hipparion are essentially similar to those of the horse, but the pattern of the 

 grinders is in some respects a little more complex, and there is a depression on the face of the skull in front of 

 the orbit, which is not seen in existing horses. 



" In the earlier Miocene, and perhaps the later Eocene deposits of some parts of Europe, another extinct 

 animal has been discovered, which Cuvier, who first described some fragments of it, considered to be a Pala'oiherium. 

 But as further discoveries threw new hght upon its structure, it was recognised as a distinct genus, under the name 

 of Anchitherium. 



" In its general characters, the skeleton of Anchitherium is very similar to that of the horse. Each foot pos- 

 sesses three complete toes ; while the lateral toes are much larger in proportion to the middle toe than in Hipparion, 

 and doubtless rested on the ground in ordinary locomotion. 



" The ulna is complete and quite distinct from the radius, though firmly united with the latter. The fibula 

 seems also to have been complete. There are forty-four teeth. The incisors have no strong pit. The canines 

 seem to have been well developed in both sexes. The first of the seven grinders, which is frequently absent, and, 

 when it does exist, is small in the horse, is a good-sized and permanent tooth, while the grinder which follows it is 

 but httle larger than the hinder ones. The Anchitherium, the Hipparion, and the modern horses, constitute a series in 

 which the modifications of structure coincide with the order of chronological occurrence, in the manner in which they 

 must coincide, if the modern horses really are the result of the gradual metamorphosis, in the course of the Tertiary 

 epoch, of a less specialised ancestral form. . When America was first discovered by Europeans, there were no traces 

 of the existence of the horse in any part of that continent. Nevertheless, the investigations of American geologists 

 have proved that the remains of horses occur in the most superficial deposits of both North and South America, just 

 as they do in Europe. Therefore, for some reason or other, the horse must have died out on that continent at 

 some period preceding the discovery of America. Of late years there has been discovered in the Western Terri- 

 tories of America a marvellous accumulation of deposits, which furnishes us with a consecutive series of records 

 of the fauna of the older half of the Tertiary epoch, for which we have no parallel in Europe. The researches of 

 Leidy and others have shown that forms alhed to the Hipparion and the Anchitherium are to be found among 

 these remains. They tend to show that we must look to America, rather than to Europe, for the original seat 

 of the equine series ; and that the archaic forms and successive modifications of the horse's ancestry are far better 

 preserved there than in Europe. The succession of forms which Professor Marsh has brought together carries us 

 from the top to the bottom of the Tertiaries. Firstly there is the true horse. Next we have the American Pliocene 

 form of the horse. In the conformation of its limbs it presents some very slight deviations from the ordinary horse, and 

 the crowns of the grinding teeth are shorter. Then comes the Protohippus, which represents the European Hipparion, 

 having one large digit and two small ones on each foot, and the general characters of the fore-arm and leg to which 

 I have referred. But it is more valuable than the European Hipparion, for the reason that it is devoid of some 

 of the pecuharities of that form— peculiarities which tend to show that the European Hipparion is rather a member 

 of a collateral branch than a form in the direct fine of succession. Next, in the backward order of time, is the 

 Miohippus, 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 of the pedigree of the horse stops here ; in the American Tertiaries, on the contrary, the 

 series of ancestral equine forms is continued into the Eocene formations. An older Miocene form, termed Mesohippus, 

 has three toes in front, with a large spUnt-Hke rudiment representing the httle finger ; and three toes behind. 

 The radius and ulna, the tibia and the fibula, are distinct, and the short-crowned molar teeth are anchitheroid in 

 pattern. 



" But the most important discovery of all is the Orohippus, which comes from the Eocene formation, and is the 

 oldest member of the equine series as yet known. Here we find four complete toes on the front limb, three toes on 

 the hind hmb, a well-developed ulna, a well-developed fibula, and short-crowned grinders of simple pattern. 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 of ancestral equine animals, we shall 

 find, first, a form with four complete toes and a rudiment of the innermost or first digit in front, with probably a 



