ae 
THE NEAREST ALLIES OF THE HORSE. 83 
two types of the group, the horse and the ass, in that the geogra- 
phical distribution of the Hquide is very marked and limited within 
certain ranges, and in that the members of the group are so striking 
and interesting as to have received a good deal of notice from tra- 
vellers and naturalists. ‘The difficulties in our way are that some 
confusion has arisen in nomenclature, that observers have not been 
exact and detailed enough either from a naturalist’s or from a horse- 
man’s point of view, that many of the Equide are very wild and 
difficult to approach, and, finally, that they are difficult of transport 
and at first intolerant of confinement in our larger zoological 
collections. The beautiful work by Cornwallis Harris on the large 
game of South Africa must be specially mentioned on account of 
its value to the naturalist and to the sportsman, and because I am 
indebted to it for some of my illustrations. 
Characters—The Kquide are odd-toed solidungulate animals in 
which the hoof -attains its highest development. Several other 
anatomical features of their limbs point to their swiftness of foot ; 
for example, the femur has a third trochanter, the two facets on the 
front of astragulus are very unequal, ‘They are all gramnivorous and 
have, accordingly, a fairly simple stomach and capacious in testine, to- 
gether with a special form of dentition not suited to rumination, but 
with well marked diastemata or breaks in the tooth series. The dorso- 
lumbar vertebree are not less than twenty-two in number, and horns 
are not present asa normal character. Among the order Ungulata, 
to which the Equidee belong, the rhinoceroses and tapirs of extant 
genera and the paleotheride and the macrauchenide of the past 
are included with the Equide as odd-toed or perissodactyla, the 
differences between the horses and other odd-toed ungulates are, 
however, very marked. All Equide are gregarious, the units of the 
herds being family groups of eight to ten, and the size of the full 
herd being determined by plentifulness of grass and freedom from 
disturbance. The habitat is country firm under foot and somewhat 
ary. There is a tendency to migrate in accordance with food sup- 
plies to the plains in wet weather and to mountains in dry weather, 
but in all countries occupied by Equide the plains are desert and 
sandy throughout a considerable part of the year. 
It will be observed that in every respect, and even in the minds 
of naturalists, there is a tendency for the different equine forms -to 
run into one another, whence has resulted much difference of 
opinion as to classification of the group. Species run into species, 
