Horse (n. p., 1893); and for bibliography, Huth, Works on Horses and Equitation, a Bibliographical Record (London, 1887).
HORSE. A miner's term, applied to any intruded material which is the apparent cause of a sudden interruption in the continuity of a mineral that is being quarried, as when a dike of igneous rock cuts across an ore body. In vein-mining a detached mass of rock or spar which fills the vein is called a horse, while colliers apply the term to the shale which replaces the coal-bed, as well as to such interruptions as seem to have been the channels of small streams, and which were subsequently filled up by the clay that formed the roof of the coal.
HORSE. On shipboard, an iron jackstay or rail used as a traveler's guide or securing bar, usually called a horse-rail. Also the old name for a foot-rope on a yard; and the secondary foot-rope at the end of a yard is still called the Flemish horse.
HORSE, Fossil. Remains of horses, often of extinct species, have been found in the cave-beds, river-gravels, bone-licks, and loess deposits of the Quaternary Period, or ‘Age of Man,’ in almost all parts of the world. In the more ancient deposits of the Tertiary Period, or ‘Age of Mammals,’ have been found remains of a series of ancestors of the horse, which illustrate the evolution of this race through this entire geological period, a time probably of some millions of years. Fossil horses of the Age of Man are much like the existing species, and are included for the most part in the same genus (Equus). They have been found in Europe, Asia, Africa, North and South America, but none in Australia or in the Oceanic islands, except in those which, like the British Isles, were joined to the continental mainland during the early part of the Quaternary Period. With these exceptions the animal was of world-wide distribution, and inhabited especially the open grassy plains and high plateaus of the interior of the great continents, at the beginning of the Age of Man. All these races were at first wild.
In the New World they became extinct. When the Spaniards first invaded the two Americas they found no horses, wild or domesticated. The Indians, who had domesticated the llama, the alpaca, and the dog, knew nothing of the horse, and were astonished and terrified at the sight of the strange and unfamiliar animals which the newcomers rode. Yet, when introduced by the white races, the horse ran wild and flourished and increased greatly in the same regions where its native cousins had formerly lived, showing how well the country was suited to their needs. Why the earlier native horses became extinct is a problem not yet solved.
In Central Asia, two wild races, Przewalsky's horse and the Asiatic wild ass, or kiang (q.v.), persist to the present day; others were domesticated by man in the earliest times, and their use in Chaldea and Egypt for draught and riding is depicted in the ancient mural paintings. In Africa the larger species became extinct, but the smaller zebras still survive in the southern part of the continent, and the African wild ass in the northern part (Somaliland).
The wild species of Europe, a small race, short-legged and shaggy-haired, was domesticated by man, for it is represented in rude prehistoric drawings scratched on bone or ivory by men of the Neolithic or Polished-Stone Age.
The domesticated horses now in use are chiefly derived from the Asiatic race, but it is probable that in some breeds there is a considerable strain of this European species or variety, and it is possible also that African races may have been domesticated and to some extent mixed with the Asiatic species. The existing wild horses of North and South America, the broncos and mustangs, are descendants of the animals brought over by the Spaniards; but it is possible that in South America some survivors of the native races still existed at the time of the discovery of the continent, and mixed with the introduced species when it ran wild.
In general, only fragmentary specimens, parts of skulls, bones, or teeth of these extinct horses have been found fossil, so that their characters are very imperfectly known. A number of complete skeletons were found in Texas in 1899, one of which was placed in the American Museum of Natural History, New York. This species, Equus Scotti, was of the size of a trotting horse, but in proportions more like a zebra, with deep jaw, short neck and legs, and small feet. Another extinct species, the Hippidiura of Argentina and Patagonia, was large-headed, with extremely short and stumpy legs and feet, exaggerating some of the peculiarities of the Shetland pony, although of larger size.
Tertiary Ancestors of the Horse. The history of the evolution of the horse through the Tertiary Period affords the best-known illustration of the doctrine of evolution by means of natural selection (q.v.), and the adaptation of a race of animals to their environment. The ancestry of this family has been traced nearly as far back as the beginning of the Tertiary without a single important break. During this long period of time, estimated at nearly three millions of years, these animals passed through important changes in all parts of the body, but especially in the teeth and in the feet, by which they became adapted more and more perfectly to that particular environment, namely, the open plains of a great plateau region with their scanty stunted herbage, which are the natural habitat of the modern horse.
Equine Characteristics. The horse (including under his name the asses and zebras, as well as the true horses—see Equidæ) is unique among modern animals in the fact that it walks on the extreme tip of the central digit of the foot, corresponding to the middle finger-nail of man, and that all the remaining toes have completely disappeared. The feet are greatly elongated, so as to equal the other segments of the limbs in length, and to raise the animal much higher above the ground than if he walked, as does a man or a bear, on the sole of the foot. In each foot the first and fifth digits (thumb and little finger) have completely disappeared and left no trace, while of the second and fourth digits only a small slender rudiment exists which represents the metapodial. or bone of the palm, and is called a ‘splint.’ These two splint-bones lie closely against the cannon-bone, or metapodial of the central digit, and are not indicated on the surface of the foot. The modern horse is therefore one-toed.
The teeth are equally peculiar. There are six grinding teeth in a closely set row on each side
