able increase in the proportionate length of the limbs, and especially of the lower part of the leg and foot. The surfaces of the joints, at first more or less of the ball-and-socket kind, permitting of free motion of the iimb in all directions, become keeled and grooved like a puiley, thus permitting free motion forward and backward, but limiting the motion in all other directions, and increasing considerably the strength of the joint. By this means the foot is made more efficient for locomotion over a smooth, regular surface, but less so over very rough ground, of little use for striking or grasping, or the varied purposes for which the feet of many-toed animals are used. The increased length in the lower leg and foot increases the length of the stride without decreasing its quickness, for the heavy muscles of the leg are chiefly in the upper part, and to increase the length of the lower part changes the centre of gravity of the limb very little, and it consequently swings to and fro from the socket nearly as fast; for in an ordinary step the leg swings like a pendulum, and the speed of the swing is regulated by the distance of the centre of gravity from the attachment, as that of a pendulum is by the height of the bob. To increase the length of lower leg and foot will therefore give the animal greater speed; but it puts an increased strain on the ankle and toe joints, and these must be strengthened correspondingly, by converting them from ball-andsocket joints to 'ginglymoid' or pulley joints. Additional strength, likewise at the expense of flexibility, is obtained also by the consolidation of the two bones of the forearm (ulna and radius) and leg (tibia and fibula) into one, the shaft of the lesser bone practically disappearing while its ends become fused solidly to its larger neighbor. Corresponding with the increase in length of limb, it is necessary for a grazing animal that the Lead and neck should increase in length in order to enable the mouth to reach the ground. So in the modern horse we find the neck and head much elongated when compared with the little Hyracotherium, and this elongation has taken place at equal pace with the elongation of the legs. The reduction and disappearance of the side toes, and the concentration of the step on the single central toe, serve likewise to increase the speed over smooth ground. The soft yielding surface of the polydactyl foot is able to accommodate itself to a rough, irregular surface, but on smooth ground the yielding step entails a certain loss of speed. An illustration is afforded by the pneumatic tire of a bicycle; a 'soft' tire accommodates itself to a rough road, and makes easier riding, but a 'hard' tire is faster, especially on a smooth road. Similarly the hard, firm step from the single toe allows of more speed over a smooth surface, although compelling the animal to pick its way slowly and with care on rough, irregular ground. The change in the character of the teeth from brachydont.' or short-crowned, to 'hypsodont,' or long-crowned, enables the animal to subsist on the hard innutritious grasses of the dry plains, which require much more thorough mastication before they can be of any use as food than do the softer green foods of the swamps and forests. All these changes in the evolution of the horse are adaptations to a life in a region of level, smooth, and open grassy plains, which are the natural habitat of the horse. The race, better fitted at first for a forest life, has become more and more completely adapted to live and compete with its enemies or rivals under the conditions which prevail in the high, dry plains of the interior of the great continents. The great increase in size, which has occurred in almost all races of animals whose evolution we can trace, is dependent on abundance of food. A larger animal, as may be shown on ordinary principles of mechanics, requires more food in proportion to its size than does a smaller one, in order to keep up a proper amount of activity. On the other hand, a larger animal is better able to defend itself against its enemies and rivals. Consequently, as long as food is abundant, the larger animals will have the advantage over their smaller brethren, and by the laws of natural selection the race will tend to become continually larger until a limit is reached when sufficient food becomes difficult to obtain, and the animal is compelled to devote nearly all its time to getting enough to eat. CAUSE OF THE EVOLUTION. The evolution of the horse, adapting it to live on the dry plains, probably went hand in hand with the evolution of the plains themselves. At the commencement of the Age of Mammals the western part of the North American continent was by no means so high above sea-level as now, great parts of it had but recently emerged, and the Gulf of Mexico still stretched far up the valley of the Mississippi. The climate at that time was probably very moist, warm, and tropical, as is shown by the tropical forest trees found fossil even as far north as Greenland. Such a climate, with the low elevation of the land, would favor the growth of dense forests all over the country, and to such conditions of life the animals of the beginning of the mammalian period must have been adapted. During the Tertiary the continent was steadily rising above the ocean level, and at the same time other influences were at work to make the climate continually colder and drier. These conditions restricted and thinned the forests, and caused the appearance and extension of open grassy plains. The ancient forest inhabitants must then either retreat and disappear with the forests, or adapt themselves to the new conditions of life. The ancestors of the horse, adopting the latter course, changed with the changing conditions, and the race became finally-as we see it to-day-one of the most highly specialized of animals in its adaptation to its peculiar environment. At the end of the Age of Mammals the continents stood at a higher elevation than at present, and there was a broad land connection between Asia and North America, as well as those now existing. At this time the horses became cosmopolitan, and inhabited the plains of all the great continents, excepting Australia. It is a question whether the direct ancestry of the modern horse is to be searched for in Western America or in the little known interior plains of Eastern Asia. It is also unknown why the various species which inhabited North and South America and Europe during the early part of the Age of Man should have become extinct, while those of Asia (horse and wild ass) and of Africa (wild ass and zebra) survive. Man since his appearance has played an important part in the extermination of the larger animals; but there is nothing to show how far he was responsible for the disappearance of the native American species of horse. PARALLEL EVOLUTION IN OTHER RACES. It is interesting to observe that while the evolution of the horse was progressing during the Tertiary period in North America another group of hoofed animals, now extinct, the Litopterna, in South America evolved a race adapted to the broad plains of Argentina and Patagonia, and singularly like the horse in many ways. These animals likewise lost the lateral toes one after another, and concentrated the step on the central toe; they also changed the form of the joint-surfaces from ball-and-socket to pulley joints; they also lengthened the limbs and the neck; and they also lengthened the teeth, and complicated their pattern; but, unlike the true horses, they could not form cement on the tooth, and it was by no means so efficient a grinder. This group of animals, native to South America, became totally extinct, and were succeeded by the horses, which immigrated from North America, which in their turn became extinct before the appearance of civilized man. Many of the contemporaries of the horse in the Northern Hemisphere, such as the camels in America, the deer, antelopes, sheep, and cattle in the Old World, were likewise lengthening the limbs, lightening and strengthening the feet, and elongating the tooth-crowns, to adapt themselves to the changing conditions around them, but none paralleled the horse's evolution quite so closely as did the pseudo-horses of South America. BIBLIOGRAPHY. Huxley, American Addresses (London, 1877); Marsh, "Polydactyl Horses, Recent and Extinct," in American Journal of Science, vols. xvii., xliii. (New Haven, 1892); Flower, The Horse: A Study in Natural History (London, 1891); Hutchinson, Creatures of Other Days (New York, 1894); Lucas, Animals of the Past (New York, 1901); Matthew, The Evolution of the Horse, No. 9 in series of Popular Guide Leaflets to the American Museum of Natural History (New York, 1902). For technical articles on fossil horses, consult the bibliography in Woodward, Vertebrate Paleontology (Cambridge University Press, 1898); and in addition Gidley, in Bulletin of the American Museum of Natural History (New York, 1900, 1901). HORSE-ANT. A popular name for certain hymenopterous insects forming the family Mutillidæ. They are also known as 'cow-ants,' 'cowkiller ants,' 'solitary ants,' and 'velvet ants.' Although they resemble the true ants, they are more closely related in structure to the social wasps, in spite of the fact that they are not winged, and are solitary in their habits. They are ferocious stingers, and are clothed with hair, which is frequently brightly colored-often bright red. In their early stages some and possibly all are parasitic in the nests of wild bees. HORSE ARTILLERY. Cannon for use with cavalry troops or flying columns of any kind where great mobility is required. In horse artillery all the personnel is mounted, and the gun is lighter than the ordinary field gun. Horse artillery must be mobile enough to keep up with the cavalry in attack and pursuit. When cavalry charges cavalry, the horse artillery takes up a position and fires upon the enemy's horse. In successful attack it follows its cavalry; in defeat it covers retirement. In the English Army, which in 1900 had 18 batteries of horse artillery in the home establishment and 11 in India, the gun used is the 12pound breech-loader, calibre three inches, firing shrapnel (q.v.), shell, and case-shot. See ARTIL LERY; FIELD ARTILLERY. HORSE-BOT. The bot-fly of the horse (Gastrophilus equi). See BOT. HORSE-CHESTNUT (so called probably from the large size of the nuts; less plausibly explained from the former use of them when ground as food for horses), Esculus. A genus of trees of the natural order Sapindaceae in which the A HORSE-CHESTNUT TWIG. leaves are large opposite digitate; flowers with five spreading unequal petals, and the capsule leathery, three-valved, and covered with soft spines. The seeds, of which there are from one to three in each fruit, are large and somewhat resemble chestnuts; but the habit of the trees, its leaves and flowers, are very unlike those of chestnuts, with which it has no botanical affinity. The common horse-chestnut (Esculus Hippocas tanum) is a much esteemed ornamental tree, very frequently planted whenever the climate is suitable, on account of its rich foliage and its erect racemes of beautiful reddish-white flowers, which are produced on the extremities of the branches, and contrast admirably with the dark green of the leaves. It is supposed to be a native of Persia or some parts of the East, and was introduced into Western Europe from Constantinople at the end of the sixteenth century. It attains a great size, sometimes rising to the height of 100 feet, and extending its branches very widely. Sometimes they droop almost to the ground. The leaves have long stalks, and five to seven obovate wedge-shaped leaflets. The wood is soft, not very strong, nor very durable in the open air; but is used for many ordinary purposes, and by carvers, turners, etc. The bark is bitter and astringent, contains a bitter principle called asculine, and has been used in tanning and dye HORSE-CHESTNUT FRUIT. ing. The seeds are unpleasantly bitter, and contain so much of the saponaceous substance peculiar to this natural order that when reduced to powder, they may be used for washing. They contain, however, a large quantity of starch, which may be extracted and freed from bitterness by means of an alkaline solution or repeated washing. This starch is prepared on a large scale and at a cheap rate in France. Horsechestnuts have long been employed in various countries as food for oxen, sheep, swine, and horses, all of which are fond of them, and grow fat upon them. In the other species of Esculus which are natives of North America the foliage is very simi lar to that of the common horse-chestnut. Both HORSE LATITUDES. See CALM LATITUDES. BILE. HORSE-MACKEREL. A name given to sevcral species of fishes of the family Carangidæ, and especially, in Great Britain, to the scad (Trachurus trachurus), and in the United States to the crevallé (Caranx hippos). The carangids are all trim, vigorous fishes, and are peculiar in that the teeth, when present, are villiform or conical. Usually the scales are very small, or they may be altogether wanting. In many instances the lateral line is entirely or partially armed with shield-like, overlapping plates. (See Fig. 2, on the Plate of HORSE-MACKEREL, acThe horse-mackerels companying this article.) are distributed over all seas except the polar, and their remains go back to Cretaceous time, while they are profusely represented in marine strata of Eocene date. They sometimes gather in enormous shoals, and are captured in vast quantities in seines. They are carnivorous, and swift and fierce in pursuit of lesser fishes.. Their flesh is excellent food. The typical genera are slender. compressed, mackerel-like fishes, but the family includes many others of different form, such as the amber-fishes (Seriola), the pilot-fishes (Naucrates), the moonfishes (Vomer and Selene), and the pompanos. These are described indiConsult vidually under their names elsewhere. Goode's American Fishes (New York, 1888); Gunther, Introduction to the Study of Fishes (London, 1880). HORSEMANSHIP. the leaves and fruit of the American buckeye (Esculus glabra) are poisonous. This tree ranges from Pennsylvania to Alabama, and west to Kansas and Texas. North America possesses a number of other species with very similar foliage, smaller flowers, and smooth fruit. In California the seeds of Esculus California are used as food by some Indian tribes, as are those of Esculus turbinata in Japan. The seeds of Esculus parviflora, the edible buckeye, are eaten, either boiled or roasted. This species is a shrub with long and beautiful racemes of fragrant white flowers, which have long projecting stamens. It is a native of the Southern States. Esculus Indica is a lofty tree which grows at elevations of 8000 to 10,000 feet in the Himalayas, and produces seeds very similar to those of the horse-chestnut, which, although bitter, are eaten in time of scarcity. HORSE-CREVALLÉ, kre-vål-lā'. See CA horses. It is to the Greeks that we must look for VALLY. HORSE FAIR, THE. A well-known painting by Rosa Bonheur, exhibited at the Salon of 1853. After passing through several hands it formed part of the Stewart collection, and was finally purchased by Cornelius Vanderbilt, and presented by him to the Metropolitan Museum, New York, where it now hangs. There are several replicas by the artist in England, and an engraving of the painting by Landseer. The canvas shows a number of horses in motion, some with riders, some led, and some free. The art of managing our first knowledge of the history of horsemanship, for when primitive man first ventured upon the back of a captured horse is, at the best, a matter of conjecture. The 'bit' could not have been known before the age of bronze, but undoubtedly the first horsemen employed a halter or thong of rawhide passed through the animal's mouth in order to direct and control it. According to the evidence of the Egyptian monuments, bit, bridle, harness, and chariot were employed; and we know from other sources that the bridles of the early horsemen of Egypt and Asia were considerably decorated with tassels, crests, and HORSE-FISH, or HORSEHEAD. See MOON- embroidery, in a manner both rich and elaborate; FISH. HORSE-FLY. See GADFLY. HORSE-FOOT SNIPE. See TURNSTONE. HORSE-GENTIAN. A North American medicinal plant. See FEVERWORT. HORSE GRENADIERS. See MOUNTED IN FANTRY. HORSE GUARDS. The military headquarters of the British Army, and the offices of the Field Marshal Commander-in-chief, War Office, Pall Mall, London, S. W. It is a term used to distinguish the purely military part of the army organization from that of the civil authority, the Secretary of State for War. The oldest cavalry regiments of the British Army are also known as the Horse Guards, the term including the Oxford Blues, first raised by the Earl of Oxford in 1660, and now styled the Royal Horse Guards, or The Blues; and the First and Second Regiments of Life Guards (q.v.), organized in 1661-62. but anything approaching the modern saddle was unknown to either Egyptian, Assyrian, or Persian. Instead, a decorated and fringed cloth fastened to the animal by a girth was employed to afford the horseman a seat. The warlike tribes occupying the northern border of Greece are credited with the introduction of horsemanship among the Greeks, among whom the art was held in very high esteem. Horse-races were a conspicuous feature of their festivals and games; a noteworthy feature in connection with which was the fact that the tact and judgment of the rider was frequently a more important factor in gaining the decision than the superiority of the horse. The Athenians were especially devoted to the art, and the rules of horsemanship, so far as the seat is concerned, did not differ in essence from the good horsemanship of to-day. That the Greeks excelled in the exercise is evident from the fact that they were in the habit of taking all sorts of leaps' (according to Xenophon), “across ditches, over walls, upon and from banks;" and in military evolutions particularly, demonstrated |