Mammalia. 267 



In its domesticated forms it is probably the most useful of 

 any order to man, as from it are derived beasts of burden. 

 Members of this order also furnish us with food (meat, milk, 

 cheese, butter), leather, etc. The domestication of the horse, 

 cattle, sheep, etc., dates so far back that we know not what 

 were the wild forms from which they have descended. The 

 ungulates are divided into two groups, according as the 

 number of toes is odd or even, the odd-toed group being 

 called Perrissodactyls, and the even-toed, Artiodactyls. 



The Perissodactyls. These forms have an odd number 

 of toes, as shown in the horse, rhinoceros, and tapir. 



The Horse. The horses now in this country are not 

 natives, but were introduced from the old world; the 

 Indians did not know the horse till after what we call the 

 " discovery " of America. Still, America did have horses 

 in earlier geologic periods, and the history of the develop- 

 ment of the horse, as shown by fossil remains (largely 

 found in this country), is exceedingly interesting. The 

 earliest form was about the size of a fox, and had four 

 well-developed toes in front, with a rudiment of a fifth 

 and three toes behind. Later appears a form with four 

 toes in front and three behind. Then came a horse about 

 as large as a sheep, with only three fully developed toes 

 in front, the fourth represented by a rudiment, but still 

 having three toes in the hind foot. Later still the outer 

 toe became reduced to a mere remnant. Then came a form 

 about the size of a donkey, with three toes all around ; 

 the middle toe persisting and the two on each side becom- 

 ing dwarfed. Finally, the one-toed horse was evolved, the 

 single toe being the middle one of the five, that is, corre- 

 sponding to our middle toes and middle fingers. 



The Tapir. The tapirs are found in South America 

 and Sumatra. They have four toes in front and three 



