Paleontology. 189 
Equus: Qua- 
ternary and 
Recent. 
Pliohippus : 
Pliocene, 
. 
Protohippus : 
Lower Ilio- 
cene, 
Miohippus : 
Miocene. 
Mesohippus: 
Lower Mio- 
cene, 
Orohippus : 
Eocene, 
Fic. 83.—Feet and teeth in fossil pedigree of the Ilorse. (After Marsh.) 
a, bones of the fore-foot ; 6, bones of the hind-foot; c, radius and ulna; 
d,libia and fibula; e, rootsof atooth; fand g, crowns of upper and 
lower mular tecth. 
