THE ALLIES OF THE SQUIRREL 421 



leisure for its digestion. The food is then raised to the mouth 

 in a somewhat softened condition and is there ground be- 

 tween the molar teeth and moistened with saliva, after 

 which it is again swallowed, this time into the psalterium, or 

 manyplies, so called from the numerous folds in its lining 

 membrane. The food slowly filters through the manyplies 

 into the true digestive stomach, or abomasum. This very 



Fig. 222. Diagram of the stomach of a ruminant 

 Arrows and dotted lines show the course of food (After Wiedersheim) 



characteristic habit of chewing the cud has suggested the name 

 of ruminants (Lat. rumen, "throat") for these ungulates. 



Most of the so-called wild horses are in reality horses 

 which have escaped from domestic breeds. The tarpan of 

 Central Asia is an exception. It seems to be truly wild, not 

 feral. This horse closely resembles the pictures of horses 

 made by man on walls of caverns and those carved on bone, 

 which date back long before the beginnings of real history. 

 The interesting story of the geological development of the 

 horse is told farther on. 



Of the Proboscidea the elephants alone require mention. 

 There are two common present-day species, the Asiatic 

 (El'ephas in'dicus) and the African elephant (Elephas afri- 



