264 MOSTLY MAMMALS 



of a hippopotamus, we shall find that in each foot the four 

 nearly equal-sized toes are severally supported by four 

 complete and distinct bones, known in the fore-limb as 

 the metacarpals and in the hind-limb as the metatarsals ; 

 and it will be obvious that this is a much simpler or more 

 generalised type of foot-structure than that which charac- 

 terises the ruminants. If, again, we contrast the foot of a 

 hippopotamus with that of a pig, we shall find that whereas 

 in the latter the lateral pair of hoofs are considerably 

 smaller than the middle pair and do not touch the ground 

 when the animal is walking on a hard surface, in the 

 former the two pairs are nearly equal in size and are all 

 applied to the ground in walking. In this respect the 

 hippopotamus is the most primitive of all the even-toed 

 hoofed mammals that have survived to the present day, 

 and is, therefore, a creature of special interest to the 

 believer in evolution. It is, indeed, a member of the great 

 group from which the ruminants are considered to have 

 originated ; although, if the reader should be led from this 

 statement to jump to the conclusion that a hippopotamus 

 was in any sense an ancestor of the giraffe, he would be 

 4ed into a grievous error. As is the case with nearly all 

 existing animals of a primitive type, the hippopotamus, in 

 place of being an ancestral form, is a side branch from 

 the original stock, which has developed certain specialised 

 features not found in the latter. To show that this is the 

 case, we have but to study the teeth of the various species 

 of hippopotami, which are of such a nature as to show 

 conclusively that those of the ruminants could not have 

 been derived from them. 



In the group of animals last mentioned the molar-teeth 

 have crescent-shaped columns on their grinding surfaces. 

 Extinct animals show a complete passage from such teeth 



