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— 
6 ,1-1 ,4—4 ,,3- 
13,03 Pp Ms 
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 Hohippus, an older 
eocene form, about as large as a fox, which had four well- 
developed toes and the rndiments of a fifth on each fore-foot, 
and three toes behind. In later eocene beds appeared an 
animal (Orohippus) of similar size, but with only four toes in 
front and three behind. In newer beds, 7. ¢., 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 (Anchithertum or Miohippus) 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 
(Pliohippus) makes his appearance. A true Hqwus, 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. 
