FAOUriOS OF THE HOliSF l\ XATlh'l:' IT) 



and also a t iii\- icMiinaut of (lie iiincnnosl oi- fust di^il . 'I'hc piopoit ions 

 of the skull. tlu> slioi't neck and aiclicd hack and the lind)s of moderate 

 length, were very lit tlo horselike - i-eealliu^on the condary, some niodeiii 

 ciirnivorous animals, ospocially the civets {Viverrida'). The teeth were 

 short-crowned and covorcd with low roundcMl kno})s of enamel, suj<K<'^t- 

 in^ those of monkeys and of pij!;s or other omnivorous animals, })ut not at 

 all Hke the long-crowned complicated grinders of the horse. 



Commencing with the Hyracothen'um, twelve stages have l)een recog- 

 nized from as many successive formations, showing the gradual evolu- 

 tion of the race into its modern form, and each stage is characteristic of 

 its particular geological horizon. Some of the stages have been found in 

 several parts of the world, but by far the most complete and best known 

 series comes from the Tertiary Badlands of the western United States. 

 Besides the main line of descent which led into the modern horses, asses 

 and zebras, there were several collateral branches which have left no 

 descendants. Of some stages all parts of the skeleton have been found; 

 of others only the jaws, or jaws and feet, are known. We can mention 

 only the more important stages. 



1 and 2.' Hyracotherium and Eohippus. Lower Eocene. The 

 Hyracotherium is the most primitive stage known, but only the skull has 

 been found, so that it has not been determined exactly what the feet were 

 like. The teeth display six rounded knobs or cusps on the upper molars 

 and four on the lower ones, and these are just beginning to show signs of 

 fusing into cross-crests. The premolar teeth have only one main cusp, 

 except the third and fourth premolars (next the molars) in each jaw, 

 which have two and three, re- 

 spectively. The only specimens 

 which have been found were in the 

 London Clay or Lower Eocene of 



England and are preserved in the ^ig- 4- Eohippus. Lower Eocene. 

 British Musemn. Upper teeth natural size. Short- 



„-_,,. . , , crowned teeth, no cement, premolars 



The Eohippus IS much better simpler and smaller than molars 

 known. It comes from the Lower 



Eocene of Wyoming and New Mexico, and is very like the Hyracotherium- 

 except that in some species the molar teeth have the cusps more clearly 

 fusing into cross-crests; the last premolar is beginning to look like one of 

 the true molars. The fore foot of this animal has four complete toes. The 

 hind foot has three complete toes and the splints of the first and fifth 

 digits can still be detected in some species. A skeleton of Eohippus 

 was found by Dr. J. L. Wortman in 1880 in the Wind River Badlands of 



iThese numbers refer to the stages in the direct line of descent of the modern horse. 

 2It is doubtful whether it is a distinct genus. 



