io;6 



THE UNGULATES, OR HOOFED MAMMALS 



The whole of the existing representatives of the horses are included 

 in the genus Equus, of which the following are distinctive character- 

 istics. In the upper cheek-teeth the portion called the anterior pillar (marked p in 

 the middle figure on p. 1075) is connected by a narrow neck of enamel and ivory 

 with the adjacent crescent in the middle of the same side of the tooth; and each foot 



has but a single toe. 

 The total number of 

 teeth in the males of 

 all the living species 

 is forty-two; these 

 comprising f incisors, 

 \ canines, and cheek- 

 teeth. The first up- 

 per tooth of the cheek 

 series, that is to say, 

 the first premolar, is, 

 however, very small 

 in all the living 

 species, and is fre- 

 quently wanting, thus 

 reducing the number 

 of teeth to forty. It 

 is, however, larger in 

 many fossil species, 

 and a few of these 

 also have a small first premolar in the lower jaw, thus bringing up the number to 

 the typical forty-four. The canines of the males are rather small and pointed, and 

 in the females are either rudimentary or wanting. When present, they are placed 

 near the incisors, but are separated by a long gap from the teeth of the cheek series. 

 The horses are such well-known and familiar animals, that it would 

 be superfluous to describe their form and appearance in detail. It may 

 be observed, however, that the ears are long, and that the tail is likewise elongated, 

 but may be either clothed with long hair throughout its length, or merely tufted 

 at the extremity. The neck carries a mane, which may be either erect or pendent, 

 and the fore-limb has a hard, naked callosity above the wrist joint. In most wild 

 species some portions, or the whole, of the body and limbs are marked with transverse, 

 dark stripes, but these disappear more or less completely in the domesticated breeds. 

 With the exception of those that have been introduced by man into 

 other regions, horses are now confined to the Old World, and are 

 especially characteristic of Africa. They may be divided into true horses, zebras, 

 and asses. 



Before, however, proceeding to the consideration of these groups, it 

 Nomenclature 



of Limbs may mention that the terms commonly applied to the vari- 



ous segments of the limbs of the members of the Horse family are not 

 the same as those used by the zoologist and anatomist. For instance, what is com- 



SIDE AND PALATAL VIEWS OF SKULL OF EXTINCT 



THREE-TOED HORSE. 



(After Zittel.) 



Form 



Distribution 



