4 ELEPHANTS. 



grinding vegetable matter and feet adapted solely for moving 

 from place to place in search of pasturage. If, however, we 

 trace back through the earlier periods of the Earth's Geological 

 History the extinct animals from which these quite distinct 

 modern groups are descended, we find that, in nearly all cases 

 in which these earlier fossil forms are well known, there is a 

 tendency for them to become more and more alike. In the 

 early Eocene, indeed (see Table 1, p. 2), the Garni vora and 

 Ungulata are not always to be distinguished from one another 



Fig. 2. 



Skull and mandible of Striped Hyaena, showing the sharp cutting cheek- 

 teeth adapted for a flesh diet. Lettering as in fig. 1. 



with certainty, so that the animals from which they and some 

 other mammals have descended may be placed in a single 

 group. Nearly all these early mammals have certain characters 

 in common: thus in most there are five toes on each foot and 

 forty-four comparatively simply constructed teeth. Characters 

 such as these are called " primitive/' and when as time goes 

 on they become gradually changed in different ways and 

 adapted for particular purposes, they are said to be more 

 "specialised." Thus in the horse the foot (fig. 3) is extremely 

 specialised, in that it has only a single complete toe instead of 



