CENOZOIC ERA. AGE OF MAMMALS. 381 



have been found. Corresponding with the Miohippus and 

 perhaps the Protohippus of the United States, was the 

 graceful tridactyl horse (Hipparion), represented in Fig. 

 343. The most remarkable animal of this time was the 



FIG. 343. Skeleton of Hipparion gracile, restored. (After Gaudry.) 



huge Dinothere, the earliest of the Proboscidians. It had 

 a proboscis, but not yet developed to the size and strength 

 which this organ attained in the mastodon and the ele- 

 phant. The singular form of the head is shown in Fig. 

 344. True monkeys were introduced in the Miocene, and 

 that most destructive of carnivores, the saber-toothed 

 tiger (Machairodus], in the Pliocene, though the genus 

 culminated in the Quaternary (see Fig. 356, page 402). 



Some General Observations on the Tertiary Mam- 

 mals ; Genesis of Mammalian Orders and Families, 

 etc. We have already said that in the earliest Eocene, 

 the great branches of the mammalian class were very 

 near together, though their point of union has not yet 



