178 THE TOWER MENAGERIE. 
there is a vacant space, which, our readers scarcely need 
to be reminded, receives the bit, the small but irresisti- 
ble instrument by means of which man has for ages 
exercised the most complete control over the services of 
these useful animals. Although purely and essentially 
herbivorous, their anatomy, as well as their habits, sepa- 
rates them most thoroughly from the Ruminants, and 
approximates them in several respects to the Pachy- 
dermatous order, with which, in spite of their many 
discrepancies, both physical and moral, M. Cuvier has 
associated them. It is needless to point out the incon- 
eruity of this union, and it would be equally so to say 
more of the general form and external characteristics of 
a group, the principal species of which are so constantly 
before our eyes. 
It may, however, be observed, that it has been pro- 
posed to divide it into two distinct genera, the one 
containing the Horse alone, and characterized by the 
flowing tail uniformly covered with long hair, by the 
absence of a line of darker coloured hairs along the 
back, and by the presence of callous protuberances on 
the hind legs as well as on the fore: the other compre- 
hending the Asses and Zebras, and distinguished by the 
tail having a brush of long hairs at its extremity only, 
by the presence of the dorsal line, and the absence of 
the protuberances on the posterior legs. Such a divi- 
sion, resting as it does on striking but not very essential 
differences, may fairly be admitted for the purpose of 
separating the genus into sections; but can hardly be 
regarded as founded on characters of sufficient import- 
ance to disunite so well marked and strongly connected, 
as well as so limited, a group. In the same paper in 
