368 UNGULATA 
Suborder PERISSODACTYLA 
This is a perfectly well-defined group of Ungulate mammals, 
represented in the actual fauna of the world by only three distinct 
types or families—the Tapirs, the Rhinoceroses, and the Horses— 
poor in genera and species, and (except in the case of the two 
domesticated species of Equus, which have been largely multiplied 
and diffused by man’s agency) not generally numerous in individuals, 
though widely scattered over the earth’s surface. Paleontological 
Fic. 151.—Bones of right fore foot of existing Perissodactyles. A, Tapir (Tapirus indicus), 
x4; B, Rhinoceros (Rhinoceros sumatrensis), x}; C, Horse (Equus caballus), x2. U, ulna; 
R, radius ; c, cuneiform ; 7, lunar; s, seaphoid; u, unciform; m, Magnum ; td, trapezoid ; tm 
trapezium.—From Flower, Osteology of Mammalia. 
records, however, show very clearly that these are but the surviving 
remnants of a very extensive and much-varied assemblage of 
animals, which flourished upon the earth through the Tertiary 
geological period, and which, if it could be reconstructed in its 
entirety, would not only show members filling up structurally the 
intervals between the existing apparently isolated forms, but would 
also show several marked lines of specialisation which have become 
extinct without leaving any direct successors. 
The following are the principal characters distinguishing them 
from the Artiodactyla. Premolar and molar teeth in continuous 
series, with massive, quadrate, transversely ridged or complex 
crowns,—the posterior premolars often resembling the true molars 
