02 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 



6 il 4-4 3-3 



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 Eoliippus, an older 



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



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



and three toes behind. In later eocene beds appeared an 



animal (Oroliippus) 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 MesoMppus, 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 (AnchWierium or Miohippus) had the same 



number of toes, but Avith 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 ProtoMppus), 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 



(Pliohippus) makes his appearance. A true HJquus, as large 



ns 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 



