382 UNGULATA 
when reintroduced by man, form curious but as yet unsolved 
problems in geographical distribution. 
Existing Species—The existing species of the genus are the 
following :— 
The Horse, Equus caballus, is distinguished from the others by 
the long hairs of the tail being more abundant and growing quite 
from the base as well as the end and sides, and also by possessing 
a small bare callosity on the inner side of the hind leg, just below 
the “hock” or heel joint, in addition to the one on the inner side 
of the fore limb above the carpus, common to all the genus. The 
mane is also longer and more flowing, and the ears are shorter, 
the limbs longer, the hoofs broader, and the head smaller. 
Though the existing Horses are not usually marked in any 
definite manner, or only irregularly dappled, or spotted with light 
surrounded by a darker ring, many examples are met with showing 
a dark median dorsal streak like that found in all the other 
members of the genus, and even with dark stripes on the shoulders 
and legs indicating “the probability of the descent of all the 
existing races from a single dun-coloured, more or less striped, 
primitive stock, to which our horses still occasionally revert.” ! 
In Europe wild Horses were extremely abundant in the 
Neolithic or polished-stone period. Judging from the quantity of 
their remains found associated with those of the men of that time, 
the chase of these animals must have been among man’s chief 
occupations, and they must have furnished him with one of his 
most important food supplies. The characters of the bones 
preserved, and certain rude but graphic representations carved on 
bones or reindeers’ antlers, enable us to know that these Horses 
were rather small in size, and heavy in build, with large heads and 
rough shaggy manes and tails, much like, in fact, the present wild 
horses of the steppes of the south of Russia. They were 
domesticated by the inhabitants of Europe before the dawn of 
history, but it is doubtful whether the majority of the animals now 
existing on the Continent are derived directly from them, as it is 
more probable that they are descendants from Horses imported 
through Greece and Italy from Asia, derived from a still earlier 
domestication, followed by gradual improvement through long- 
continued attention bestowed on their breeding and training. 
Horses are now diffused by the agency of man throughout almost 
the whole of the inhabited parts of the globe, and the great modifica- 
tions they have undergone in consequence of domestication and 
selective breeding are well exemplified by comparing such extreme 
forms as the Shetland pony, dwarfed by uncongenial climate, the 
thoroughbred racer, and the London dray-horse. In Australia, 
! Darwin, Variation of Animals and Plants under Domestication, 1868, vol. 
i. chap. ii. 
