302 



HISTORICAL PALEONTOLOGY. 



developed that they now reach the ground. The first digit 

 (thumb or great toe) is still wanting ; as also is the fifth digit 



Fig. 230. — Skeleton of the foot in various forms belonging to the family of the Eq^iidcF. 

 A, Foot of 07-ohippiis, Eocene ; B, Foot of Anckitheriujii, Upper Eocene and Lower 

 ^Miocene ; C, Foot of HiJ>J>arion, Upper Miocene and Pliocene ; D, Foot of Horse 

 {Eqjiiis), Pliocene and Recent. The figures indicate the numbers of the digits in the 

 typical five-fingered hand of Mammals. (After Marsh.) 



(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 "svas not larger than a fox — the 

 foot (fig. 230, A) carries /t?//r toes, all of which are hoofed and 

 touch the ground, but of which the third toe is still the largest. 

 Theyf;^/ 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 som^e cer- 

 tainty, to some still older example of the EquidcB, in which 

 the first digit is developed, and the foot assumes its typical 

 five-fingered condition. 



Passing on to the Even-toed or Artiodadyle Ungulates^ no 

 representative of the Hippotamus seems yet to have existed, 

 but there are several forms {Cheer op ota77ius, Hyopota7tius^ &c.) 

 more or less closely allied to the Pigs {Sjnda)-, and the 

 singular group of the AnoplotheridcE may be regarded as form- 

 ing a kind of transition between the Swine and the Ruminants. 

 The Atioplotheria (fig. 231) were slender in form, the largest 

 not exceeding a donkey in size, with long tails, and having the 

 feet terminated by two hoofed toes each, sometimes with a 

 pair of small accessory hoofs as well. The teeth exhibit the 



