2 INTRODUCTION. 



the other to Ruminantia : but Baron Cuvier, follow- 

 ing at first the same distribution, finally made the 

 genus horse one of the pachydermous order, and 

 leaving it undivided, fixed the location .last in that 

 series, and immediately before Camelus, which con- 

 stitutes the first of the next. 



Mr. Gray, in the Zoological Journal, Vol. I., 

 defines the family of Equidse as distinguished from 

 .all other animals by the form of the hoof being un- 

 divided, the stomach simple, and the female having 

 two teats on the pubes : the teeth are, incisors f , 

 canines in the males ^-|, molars f-f=40. He 

 further divides Equidae into two genera: namely, 1st, 

 the horse; .(Equus Caballus;) and 2d, the ass; 

 (Asinus;) embracing Hemionus, the common ass, 

 .and the zebras ; the former type being destitute of 

 stripes, having warts or callosities on both arms and 

 legs, and the tail furnished with long hair up to the 

 root, while the .latter are .generally white, more or 

 less banded with blackish brown, and always have a 

 distinct dorsal line ; .the tail furnished with a brush 

 only at the extremity, and warts existing on the 

 arms alone. These distinctions have been considered 

 by M. Lesson, insufficient to constitute two genera ; 

 .and although Mr. Bell supports the views of Mr. 

 Gray, and justly contends that several of them are 

 structural, we do not admit all the facts of either 

 .naturalists as unexceptionable to the extent required 

 to constitute separate genera ; there being in reality 

 .not two, but three types or distinct groups, as will 

 .be shewn in the sequel; and exceptions to uni- 



