ANIMALS OF LONG AGO 



355 



and, in addition, the remains of another, or fifth toe on the fore feet. 

 Higher in the strata was found the Orohippus (literally, the moun- 

 tain horse, so named on account of being found near the Rocky 

 Mountains). This animal (also called the Hyracotherium) was 

 larger than the Eohippus — about the size of a Fox — it had the same 

 number of complete toes, but no remnant of a fifth. Passing from 

 the Eocene to the higher Miocene rocks a somewhat larger animal 

 was discovered and called the Mesohippus (Middle Horse); it had 

 three toes to the fore, in addition to a large splint of bone, and 

 three toes behind. This corresponds with the European Anchi- 

 therium, although there are points of divergence. Next in order, 

 and found in the lower strata of the Pliocene rocks, was unearthed 

 the Protohippus (First Horse). In this animal the centre toe, or 

 digit, of each foot was large and evidently got the work to do, 

 while there were two digits, quite small, with their tips above the 

 level of the big central digit : a European specimen presenting 

 similar features has been called the Hipparion. The Protohippus 

 was larger than its Miocene ancestor. It was the size of a Donkey. 

 In the higher Pliocene strata discovery was made of another link 

 in the chain of development, in the remains of the Pliohippus 

 (Pliocene Horse). The foot of this animal differed from that of 

 the modern Horse in some small details. At the top of the Tertiary 

 rocks remains of the true Horse are found. 



In order to give the reader a clearer view of these remarkable 

 facts it may be well to present them in tabular form. 



I. Eohippus 



i. Orohippus, or 

 Hyracotheriu m 



3. Mesohippus 



4. Protohippus 



5. Pliohippus 



6. The Modern Horse 



A A 2 



Strata. Description. 



Eocene Four toes on front feet, three on the back. 



Traces of a fifth digit on the fore feet. 

 Size of a small Fox. 



Higher Eocene As above, but minus remains of fifth digit. 

 Size of ordinary Fox. 



Lower Miocene Three toes on all four limbs. A large 

 splint of bone on front limbs. Similar 

 to European Anchitherium. 



Pliocene One large digit and two small ones. The 



small ones not touching the ground. 

 Corresponds to European Hipparion. 

 Size of a Donkey. 



Pliocene Bigger than Protohippus, feet much the 



same as modern Horse. 



