researches to form as to the outward appearance of Paloeotherium magnum.  Recent discoveries, however, have rendered it probable that this restoration is in some important respects inaccurate.  Instead of being bulky, massive, and more or less resembling the living Tapirs in form, it would rather appear that Paloeotherium magnum was in reality a slender, graceful, and long-necked animal, more closely resembling in general figure a Llama, or certain of the Antelopes.

[Illustration:  Fig. 229.—­Outline of Paloeotherium magnum, restored.  Upper Eocene, Europe. (After Cuvier.)]

The singular genus Anchitherium forms a kind of transition between the Paloeotheria and the true Horses (Equidoe).  The Horse (fig. 230, D) possesses but one fully-developed toe to each foot, this being terminated by a single broad hoof, and representing the middle toe—­the third of the typical five-fingered or five-toed limb of Quadrupeds in general.  In addition, however, to this fully-developed toe, each foot in the horse carries two rudimentary toes which are concealed beneath the skin, and are known as the “splint-bones.”  These are respectively the second and fourth toes, in an aborted condition; and the first and fifth toes are wholly wanting.  In Hipparion (fig. 230, C), the foot is essentially like that of the modern Horses, except that the second and fourth toes no longer are mere “splint-bones,” hidden beneath the skin; but have now little hoofs, and hang freely, but uselessly, by the side of the great middle toe, not being sufficiently developed to reach the ground.  In Anchitherium, again (fig. 230, B), the foot is three-toed, like that of Hipparion; but the two lateral toes (the second and fourth) are so far developed that they now reach the ground.  The first digit (thumb or great toe) is still wanting; as also is the fifth digit (little finger or little toe).  Lastly, the Eocene rocks have yielded in North America the remains of a small Equine quadruped, to which Marsh has given the name of Orohippus.  In this singular form—­which was not larger than a fox—­the foot (fig. 230, A) carries four toes, all of which are hoofed and touch the ground, but of which the third toe is still the largest.  The first toe (thumb or great toe) is still wanting; but in this ancient representative of the Horses, the fifth or “little” toe appears for the first time.  As all the above-mentioned forms succeed one another in point of time, it may be regarded as probable that we shall yet be able to point, with some certainty, to some still older example of the Equidoe, in which the first digit is developed, and the foot assumes its typical five-fingered condition.

[Illustration:  Fig. 230.—­Skeleton of the foot in various forms belonging to the family of the Equidoe.  A, Foot of Orohippus, Eocene; B, Foot of Anchitherium, Upper Eocene and Lower Miocene; C, Foot of Hipparion_, Upper Miocene and Pliocene:  D, Foot of Horse (Equus), Pliocene and Recent.  The figures indicate the numbers of the digits in the typical five-fingered hand of Mammals.  (After Marsh.)]