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602 ZOOLOGY. 



to Africa and the East Indies. The skin is remarkably thick 

 and dense, while these animals have either one or two long 

 median horns growing from the skin of the nose. A rhinoc- 

 eros contemporary with early European man formerly inhab- 

 ited England, France, and Germany, and extended into Si- 

 beria. 



A number of fossil forms lead up to the family compris- 

 ing the horse, ass, zebra, and quagga, etc., in which there 

 is a single toe, being the third on each limb. Their den- 

 tion is 



The genealogy or series of ancestral extinct Ungulates 

 leading from tapir-like forms to the modern horse has been 

 worked out partly by Huxley, and especially by Marsh, who 

 has with Leidy discovered a large series of remains in the Ter- 

 tiary beds of central and western United States, America being 

 the original home of the horse. The earliest member of the 

 series directly leading up to the horse was Eohippus, an older 

 eocene form, about as large as a fox, which had four well- 

 developed toes and the rudiments of a fifth on each fore-foot, 

 and three toes behind. In later eocene beds appeared an 

 animal ( OroJiippus) of similar size, but with only four toes in 

 front and three behind. In newer beds, i. e., lower miocene, 

 are found the remains of Mesohippus, which was as large as 

 a sheep and had three toes and the splint of another in each 

 fore-foot, with but three toes behind. In later miocene beds 

 another form (Anchitherium or Miolrippus) had the same 

 number of toes, but with the " splint bone of the outer or fifth 

 digit reduced to a short remnant." The splint bones, then, 

 represent two of the digits of several-toed animals. The suc- 

 ceeding forms were still more horse-like. " In the Pliocene 

 above, a three-toed horse (Hipparion or Protohippus), about 

 as large as a donkey, was abundant, and still higher up a near 

 ally of the modern horse, with only a single toe on each foot 

 (Plioliippus) makes his appearance. A true Equus, as large 

 as the existing horse, appears just above this horizon, and 

 the series is complete." (Marsh.) Fossil horses extended 

 over portions of North and South America, but became ex- 

 tinct before the present Indians appeared. 



