HORSE. 232 HORSE-CHESTNUT. the disappearance of the native American species of horse. Parallel Evolution is Other Races. It is intcrc-'tinp to obsor'e that while the evolution of the hor^e was pro<;ressin;; <lurin;; tlie Tertiary period in North America another group of hoofed animals, now extinct, the Litopterna, in South America e%-olved a race adapted to the broad plains of Argentina and Patagonia, and singu- larlv like the horse in many ways. These ani- mals likewise lost the lateral toes one after an- other, and concentrated the st^p on the central toe: Ihey also changed the form of the joint-sur- faces 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 ani- mals, native to South America, became totally extinct, and were succeeded by the horses, which immigrated from North .-Vmerica, which in their turn became extinct l)eforc the appearance of civilized man. JIany of the contemporaries of the horse in the Northern Hemisphere, such as the camels in America, the deer, antelopes, sheep, and cattle in the Clld World. Avere likewise length- ening 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 pstudo-horses of Sotith .mericn. 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 yaiural History (London, 1891) ; Hutchinson, Creatures of Other Days (New York, 1894) : Lucas, .4iitHio(s of the I'ast (New York, 1901); Matthew. The Evolu- tion of the Horse. No. 9 in series of Popular Guide Leaflets to the American Museum of Nat- ural History (New York, 1902). For technical articles on fossil horses, con- .sult the bibliography in Woodward. Vertebrate Palaeontology (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 hymenopternus insects forming the family Mutil- lidir. They are also known as 'cow-ants,' 'cow- killer ants.' 'solitarj- 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 ne^ts of wild bees. HORSE ARTIXLERY. Cannon for use with cavalrj- troops nr Hying columns of any kind where great mobility is required. In horse artil- lery all the personnel is mounted, and t'ne pun is lighter than the ordinary field pun. Horse artillery must 'ne 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 suc- cessful 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 establish- ment and 11 in India, the gun used is the 12- pound breech-loader, calibre thrw inches, tiring shrapnel (q.v.), shell, and case-shot. See Artil- lery; Field .■Vrtillkhy. HORSE-BOT. The bot-rty of the horse ( Qaa- trophHus Kyiii). See Hot. HORSE-CHESTNUT (so called probably from the large size ol the nuts; less plausibly ex- plained from the former use of them when ground as food for horses), JEseulus. A genus of trees of the natural order Sapindacex in which the £ A H0B8E-CIJE8TM:T TIVIU. leaves are large opposite digitate ; flowers with five spreading unequal petals, and the capsule leath- erj-, 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 verj' unlike those of chestnuts, with which it has no botanical atfinity. The common horse-chestnut (.Esculus Bippocas- tanum ) is a much esteemed ornamental tree, very frequently planted whenever the climate is suit- a'ole, 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 preen of the leaves. It is sup- posed 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 extend- ing 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 hark is bitter and astringent, contains a bitter principle called <csculine. and has been used in tanning and dye- A!i^,o,'J,,//.'.^ HORSE-CHE^TSUT FROT.
