PEDIGREE OF MAMMALS. 275 
of the aboriginal genus is repeated, and Philogenesis is 
unequivocally expressed in Ontogenesis. The Anchi- 
therium is a three-toed horse, in which, however, the 
middle toe has already undertaken the chief task. But 
in the Hipparion the two side toes are entirely raised 
from the ground, and by disuse are brought to the con- 
dition of arrest which is completed in the horse. 
In the constitution of the molar teeth the tapirs have 
remained most faithful to the ancestral type. The cir- 
cumstance that the tapir has four toes in front, whereas 
the Paleotheridz known to us, have three shows, how- 
ever, that the genus Palzotherium cannot have been 
the ancestral stock of the tapirs. For the supposition 
that the tapir acquired the fourth toe is contrary to all 
experience respecting the formation of the extremities. 
Rhinoceroses are also four-toed in front, and their close 
kindred with the tapirs is testified by the structure of 
their toes and a series of details in the skeleton. 
Hippopotami. Pigs. Tragulidze. Deer. Antelopes. Oxen. 
Anoplotheridee. 
An isolated branch of the Paleotheridze seems to be. 
the fossil genus Macrauchenide, which combines the 
