we are to continue the plan of defining the various families of Mammalia.
The genus Equus[[143]] contains not only the Horse, but the Asses and Zebras. The genus is to be distinguished as regards external characters by the following features:—The body is thickly clothed with hair; there is a more or less bushy tail and mane; the colours are apt to be disposed in stripes of black or blackish upon a yellowish brown ground; this is of course best seen in the Zebras, but the wild Asses also have some traces of it, if only in the single cross-bar of the African Wild Ass, and it is even "reversionary" in the domestic Horse at times. There are no horns upon the forehead or elsewhere; the fore-limbs or both pairs have a callous pad upon the inside, which is possibly to be looked upon as an aborted gland, possibly originally of use as secreting some odorous substance calculated to enable strayed members of the herd to regain their companions. The terminal phalanx of each of the (functionally) single digits is enclosed in a large horny hoof.
The main internal features of structure which divide this genus of Perissodactyles from the Rhinoceros or the Tapir, or from both, are: the existence of strong incisors, three on each side of each jaw; there are canines, but these are small and do not always persist in the full-grown mare. They are popularly known as "tusks" or "tushes." The first of the four premolars (the "wolf tooth") is small and quite rudimentary; it is often absent. As there are three molars, the present genus has the "typical" number of the Eutherian dentition, i.e. forty-four. In the skull the orbit is—as it is not in Tapirs and Rhinoceroses—completely encircled by bone. There is but one functional finger and toe on each hand (Fig. 121 C) and foot; the second and third digits are represented by mere splints, one of which may as an abnormality be enlarged, and reach nearly as far as the well-developed digit. There are even occasionally traces of digit number two.
The Horse, E. caballus, is to be distinguished from its congeners by the small callosities on the hind-limbs which it possesses in addition to the larger ones on the fore-limbs. The hairy covering of the tail is more abundant, as is also the mane. The head too is proportionately smaller, and the general contour
more graceful. Though Zebra markings are not usual upon E. caballus, there are plenty of examples of—what we may perhaps in this case term—a "reversion" to a striped state. The celebrated "Lord Morton's mare,"[[144]] whose portrait hangs in the Royal College of Surgeons, is an interesting case of this. It was as a matter of fact thought to be an example of that rather doubtfully-occurring phenomenon, "telegony." Its history is briefly this. The animal was the offspring of a mare that had previously produced to a male Quagga a hybrid foal. Afterwards a second foal was produced by the same mare to an Arab sire. This foal, the one in question, was striped, and hence was thought to be an example of male prepotency. But instances are known of unquestioned Horses which show the same stripes, such as a Norway pony which had not even seen a Zebra!
A last remnant of the naked palm of the hand and sole of the foot is left in the shape of a small bare area, smaller in the Horse than in the Asses, known technically as the "ergot," the term being that of the French veterinarians. As already mentioned, the Horse differs from the Asses and Zebras in the fact that the hind-limbs have callosities on the inner side. They are known as "chestnuts," and their nature has been much disputed. It has been suggested that they are the last rudiment of a vanished toe; but in all probability they are, as already suggested, traces of glandular structures, which are common, upon the limbs in many animals (see above, p. [12]).
It is a singular fact that there are apparently no wild Horses of this species. The case is curiously analogous to that of the Camel, which also is only known as feral or domesticated. Why the Horse should have become extinct as a wild animal, considering that when it does run wild it can thrive abundantly, is impossible to understand. Sir W. Flower thinks[[145]] that "the nearest approach to truly wild horses existing at present are the so-called Tarpans, which occur in the Steppe country north of the sea of Azov between the river Dnieper and the Caspian. They are described as being of small size, dun colour, with short mane and rounded obtuse nose." But he adds that there is no evidence to prove whether they are really wild. In favour, however, of their possibly being wild and indigenous European Horses, may be
mentioned the fact that their general build and appearance is highly suggestive of the wild Horses sketched by primitive man upon ivory.
A really wild Horse, and possibly the ancestor of the European domestic Horse, is E. przewalskii of the sandy deserts of Central Asia. This animal has been believed to be a mule between the Wild Ass and a feral Horse; but if a distinct form, and probability seems to urge that view, it is interesting as breaking down the distinctions between Horses and Asses. The species possesses the four callosities of the Horse, but has a poorer mane and an asinine tail.
There is no question that the Horse has been a domestic animal for very many centuries. Hieroglyphics appear to show that the Egyptians had not originally domesticated the Horse; it seems to have been first introduced among them by the Hyksos or Shepherd Kings.[[146]] Whatever the date may be, it is certain that considerably anterior to the Egyptians the Assyrians and Phoenicians possessed Horses. In Western Europe the date of the introduction of the Horse seems to have been during the bronze epoch. Lord Avebury[[147]] has pointed out that out of eighteen cases of graves in which the remains of Horse were found, twelve contained metal implements, i.e. 66 per cent. This does not of course prove that the Horse was domesticated at that period, but it throws doubt upon the earlier occurrence of the Horse in abundance. The Horse, however, does occur on the Continent associated with the remains of man during the Quaternary period.[[148]]