150 THE MAMMALIA. 



with this bird, and the nature of the locality where 

 it was discovered, justify the expression of ' sub- 

 fossil ' which is given to the species. It lived on 

 the threshold between the Diluvium and the Pre- 

 sent. And even granting that Madagascar and 

 Africa were at one time connected by land, their 

 separation must, nevertheless, have taken place 

 early in the Tertiary, and accordingly the stability 

 of the genus Hippopotamus is also proved from a 

 geological point of view. It is not only the form- 

 ation of the foot that points to very ancient pri- 

 mary forms to be looked for beyond the Tertiary 

 period ; but the dentition also which had special- 

 ised even before the separation of the family into 

 the African and the Madagascar species has varied 

 only to a very small extent. 



3. THE RUMINANTIA, OR CUD-CHEWING ANIMALS. 



After setting aside the, at present, very subor- 

 dinate group of pig-shaped Pair-hoofed animals, 

 and the Hippopotamus, all the remaining forms 

 of this division belong to the Ruminants. As all 

 are, for the most part, lively and nimble animals, 

 they do not, while grazing, take proper time to 

 masticate their food sufficiently, but hurriedly stuff 

 their paunch full of provision and then retire to 



