16 



AMK/^ICAX Mr SKIM crihE LKAFLKTS 



A\ yoiiiin^, and was dcscrihcd hy Frotcssor ( 'ojx' in ISSo. It was until 

 recently the only skeleton known of a four-toed hoise, and is well known 

 to tlu' scientific world. It was purchased hy the trustees of the .\inerican 

 Museum in \S\)A and is now on exhibition. ^'» 



A second skeleton found hy the Museum expedition of 1910. is of a 

 larpM- species, hut not advanced in any other respect. It is mounted in a 

 grazing attitud(\ and prol)ai)ly represents the general appearance of 

 Eohippus more truly than the ( 'ojx' skeleton. A third imperfect skeleton 

 secured in 191 1 is intei'estinjr as it shows the tiny splint hone of the inner 

 (li^:it of the hind foot, indicated hy facets in other specimens but not 

 actually found hefoi'e. Crushed skulls, jaws and fragments of skeleton 

 l)ones of thousands of individuals have heen found in the Lower Eocene 

 formations. 



3. Orohippus. Middle Eocexk. In this animal the splints of the 

 first and fifth dipts of the hind foot have disappeared, but there are still 

 four complete and usable toes in the fore and three in the hind foot. The 

 crests on the molars are a little clearer and the last premolar has become 

 almost like the molars, while the next to the last premolar is partially 

 molariform. A skeleton of Orohippus, discovered by Mr. Walter Granger 

 of the ^luseum expedition of 1906, in the Bridger Badlands of south- 

 western Wyoming, is exhibited next to the Eohippus skeleton. It shows 

 an animal of the size of a small dog and proportioned much Hke the breed 

 known as the whippet. 



The Orohip})us was of about the same size and proportions as some 



of the pigmy antelopes or 

 diiikerboks (Cepholophus), which 

 live in the open forests and 

 brush count ly of East and South 

 Africa, and have gained their 

 name from the quickness with 

 which they can (five or "duck" 

 into the tall grass and jungle on 

 the ajiproach of danger. 



4. Epihippus. Upper 

 Eocene. Of this stage of the 

 evolution of the hor.^e only in- 

 complete specimens have been 

 found. The molar teeth have the 

 once round cusps almost com- 

 pletely converted into crescents 

 and crests, while another tooth of the premolar series has become like 

 the molars. The toes are still foiu' in the fore foot and three in the hind 



Fig. 5. Orohippus. Middle Eocene. 

 Upper teeth, natural size. Short-crowned 

 teeth, no cement, fourth premolar like 

 molars 



Fig. G. Epihipjfu.s\ l'i)per Eocene. 

 Upper teeth, natural size. Short-crowned 

 teeth, no cement, third and fourth pre- 

 molars like molars 



