10 THE HOKSE. 



various parts it has come to be the very singular and 

 highly specialized animal we have now before us, so 

 distinct from all existing forms of life that in most 

 of the older zoological systems it was (at least asso- 

 ciated only with some very immediate allies, struc- 

 turally almost identical) placed in an order apart 

 from all other mammals, under the name of Solid- 

 ungula, Solipedia, or Nonodadyla, the animal with 

 the solid foot, or rather with a single toe on each ex- 

 tremity. 



As will be seen from the sequel, the various 

 forms of asses and zebras only differ from the horse 

 in slight details of their organization, arid with it 

 form a group entirely apart from all other existing 

 animals, a group constituting the genus Equus and 

 the family Equidce, but no longer considered so 

 isolated as to form a distinct order. In much of 

 what follows the term " Horse," unless the contrary 

 is especially stated, must be understood to include 

 the other members of the family. 



To understand the natural place of the horse in 

 the zoological system it will be necessary to take 

 a wide glance at the whole great group to which 

 it belongs. That it is a vertebrate animal, and 

 that it occupies a place in the class Mammalia, 

 no one will doubt. Within that class there can also 

 be no doubt about its taking its place in the great 



