132 THE OLDEST MAMMALS. 



deer and horns in the rhinoceroses and oxen, while pigs 

 and hippopotami gradually acquired the enormous tusks 

 with which their existing representatives are armed. 



Seeing, then, that it was not till the advent of the 

 Tertiary period that, mammals assumed the position of the 

 dominant forms of life, Cuvier's memorable discovery in 

 the second decade of this century that the class dated from 

 the middle of the Secondary period has in no essential 

 respect served to dispossess the first-named epoch from its 

 claim to the title of the AGE OF MAMMALS. 



