HORNS. Under this term are eommonly con fused two very distinct structures forming out growths on the head of ungulate animals, to which order they are confined. The word ought not, strictly, to include the bony antlers of deer or the giraffe, since these, although to a certain extent epidermal outgrowths, consist of true bone built up from blood deposits. and are not at all transformed cuticle or 'horn.' Neverthe less, as Beddard points out (in Ifammalia, Lon don, 1902), the difference is one of degree rather than of kind. The simplest condition is seen in the giraffe, each of whose paired horns is a straight, bony outgrowth, the os eornu, originally separate from the skull, but becoming, permanent ly fused with it early in life, and is covered with wholly unmodified furry skin. In deer there is the same os cornu, which may here he branched, and never becomes fused with the skull, but, on the contrary, is shed and renewed annually. and is covered with a skin modified into 'velvet' (see DEER) which decays and drops off as soon as the horn-core (antler) is perfected. Between these two falls possibly the extinct Sivatherium (q.v.). and certainly the modern pronghorn (q.v.). Here the bony core (as eornu) is fixed as in the giraffe, but begins to be branched as in the deer: and it is covered by a sheath formed of agglu tinated hairs, the hairy skin beginning from the tip of the horn and proceeding downward. gradu ally transforming into perfect horn, which is shed and renewed annually. This is an isolated ease, but connects the giraffe and (leer with the Bovidas. or proper 'hollow-horned' ruminants (Cavi cornia ). in this family the males of every spe cies, and in most eases the females also, possess upon the top of the skull protuberances of hone into which air-cells often extend from the frontal sinuses. These are eat' d 'born-cores,' and form the support of the eornubus sheaths that cover and often extend far beyond them. They are not present at birth, for obvious reasons, but begin to grow immediately afterwards. The horn sheaths grow with them, and continue even after they have reached normal size to push out at the base as fast as they wear away at the tip. Their form and position on the head is characteristic of each group: round and lateral in the oxen; slender, retrocurved or twisted, and somewhat compressed or sharply keeled in most antelopes; heavy, cross-ridged, triangular in section, and often spiral in the sheep and goats, and so on.
Evolutionists regard horns as, in most cases, a, secondary sexual character. An examination of the fossil history of the tribe shows that these appendages have been gradually acquired. and it is only recently that the females of many forms, now provided with small horns, have acquired them by heredity. Aloreove•, castration or injury to the reproductive organs is likely to affect the growth and size of the horns. Lastly, among the deer, where the does (except in the reindeer) are hornless, these appendages are acquired just pre vious to the mating season and are dropped when the breeding season is over. Their service as weapons of defense and offense is, therefore, large ly, if not primarily, in contests with each other for the supremacy of the herd—that is. in the combative process of sexual selection. They are, nevertheless, in many instances, powerful weap ons in resisting and attacking outside enemies. The spear-like thrusts of the lowered horns of an enraged sable, or other large, long-horned ante lope, are feared even by lions and leopards, which than once have been killed by them. The goring power of a bull is irresistible. A heavy sheep, armed with its great horn-coils, is a 'bat tering-rain,' indeed, not to be despised. Many, however, seem to lie ornaments rather than weapons of value; or tools helpful in various ways, as snow-shovels, for one pertinent example, among the reindeer. Some of the great extinct ungulates of Tertiary time had very powerful horns, especially Coryphodon and the group of great Dinocerata, where in some cases a pair upon the forehead was supplemented by one or a pair on the snout. At present, a ruling dis tinction between the artiodaetyls and perisso dactyls is, that in the former the horns are al ways paired (in one modern case, Tetraceros. two pairs) and on the forehead; while in the latter they are set on the nose, and arc single or two in number, one behind the other. This is the case with the rhinoceroses (of which one very early form only had a paired arrangement). where the horn is a growth from the skin of the nose, composed of a solid mass of agglutinated hairs, based upon a knob of the underlying nasal bones.