254 



FIRST LESSONS IN ZOOLOOT. 



series of creatures which fill up more or less completely the 

 gap between it and the tapir. In the Tertiary deposits of 

 the Western plains have been found over twenty species, 

 forming a series from an animal about the size of a fox, 

 with four toes and the rudiments of a fifth on the fore limbs, 

 and three toes behind, up to horse-like forms of the size of 

 a sheep, until in the uppermost beds we have the Hip- 

 parion, with three usable toes, which was about as large 

 as a donkey; finally, the horse was preceded by a near ally 

 with but a single toe, the two others reduced to " splint " 

 bones, those of the modern horse representing the two usa- 

 A B ble toes of his Tertiary three-toed 



predecessor. We thus see that the 

 modern one-toed horse, so well 

 adapted for use by man, affords a 

 marked example of that process of 

 intelligent, beneficent selection of 

 farored, useful types -which has 

 gone on from early geological times. 

 The Even-toed Hoofed Mammals. 

 — These are the pig, hippopotamus, 

 and those cloven-footed beasts which 

 chew the cud. The pig and hippo- 

 potamus are not remote allies, the 

 latter having been considered as 

 "intermediate between an over- 

 ^"^ grown hog and a high-fed bull with- 



out horns and with cropped ears." But while the pig is 

 cloven-footed and clothed with bristles, the hippopotamus 

 has four toes and the thick skin is naked. 



The Ruminants. — While these cloven-footed beasts 

 (Fig. 355), comprising the deer, sheep, ox, and camel, are, 

 as regards their feet and teeth, adapted for a grazing life, 

 the adaptation is rendered still more perfect by the nature 

 of the digestive organs. 



The stomach (Pig. 253) is divided into at least three, 

 usually four, compartments, i.e., the paunch, the reticulum 



Fio. 253.— A, fore foot of Pig. 

 B, Ox. Lettering as in Fig. 



