Horn , a modification of the epidermis, presenting the same structure, whether in the nails of man, the claws of the carnivora and birds, the hoofs and horns of ruminants, the spines of the porcupine and hedgehog, the plates of the armadillo, the whalebone of cetaceans, the quills of birds, or the shell of tortoises. The horns of the stag and other deciduous antlers, strictly speaking, are not horn, but true bone, belonging to the dermal or exo-skeleton, and shed by a process of absorption at the root analogous to that by which dead bone is cast off in necrosis. Horn is composed of hardened albumen, gelatine, and a small portion of phosphate of lime. Its structure is a modification of epidermic cells, harder dried, more firmly adherent, and in which the nucleus is generally invisible; the cells are arranged in regular layers, each indicating a period of growth, and are marked by perceptible striae. The above named horny tissues arc generally attached at the base to the dermis, and are removed with the skin; they are constantly growing and wearing away, and are liable to various deformities from accidental circumstances; and the younger cells may contain pigment matter. Sections of horn under the microscope are very beautiful when seen by polarized light.

The horn of the rhinoceros, as already stated in the article Hair, in its essential character is a mere bundle of hairs; the substance erroneously called whalebone, formed by the lining membrane of the whale's mouth, has no connection with the bony skeleton, but is a horny tissue, composed of fibres whose central portion, like the medullary substance of hair, contains easily recognizable cells. In the ox, sheep, and the hollow-horned ruminants, there is a central core of bone upon which the horns are moulded. - Horn in its many varieties is adapted to numerous useful purposes; and it is an article of trade, horns and hoofs of cattle being largely exported from South America, southern Africa, and Russia. The horns of the buffalo are brought from the East Indies. From the most remote periods horns have been applied to various uses. The Egyptians and Hebrews made of them musical instruments. The Latin name cornu was also the name for trumpet, and the English name retains the same application, even if the instrument be made of brass or silver. The form of the horn adapted it for a drinking utensil, and the word is still sometimes employed in a manner to suggest this application. Horn was anciently employed for bows, and sometimes for scale armor. It also served instead of glass for windows.

The methods now in use for working horn are described in Holtzapffel's "Mechanical Manipulations." The bony horns of the deer, being cellular within, are used only in their natural forms, so as not to expose their internal structure*. They are sawn and filed into the shapes required for handles of knives and other implements. The horns particularly adapted for being converted into useful shapes are those of the ox, antelope, goat, and sheep kinds, which by reason of their laminated structure are readily separated into layers. They contain just enough gelatine to admit of their being softened by the application of less heat than is required for melting lead. The material may then be cut open with knives or shears, flattened into plates, divided into leaves, and finally struck between dies like metal. The first step in the treatment of horn is to separate the bony core. For this purpose it is macerated several weeks in water, which causes the lining membrane to putrefy, so that the core will fall out. This is burned, to make the bone earth used for cupels in assaying. The solid tip of the horn is sawn off, and is reserved for handles for knives, umbrellas, etc, and for buttons.

The remainder, either cut into short lengths or entire, is softened by immersion in boiling water, and then by heating in the flame of a fire nearly to the temperature of melted lead. The pieces, unless intended for horn cups or similar objects, are then split open with a sharp-pointed knife, and spread out flat. A solid block of iron with a conical hole, and an iron plug to fit it, are also used to open horns without endangering the scorching of them. Both being heated to the right temperature, the horn slit with a knife is inserted in the hole, and the plug driven into the horn with a mallet. In a minute it is sufficiently softened to be easily opened. The pieces, now called flats, are laid between boards, or between heated iron plates, and subjected to pressure. The amount of this for general purposes, as for combs, is moderate, for much pressure tends to make the horn split into thin laminae. But if thin plates are to be made, such as are used for lanterns, a heavy pressure is required, and if the horn is light-colored this increases its transparency. Such plates, when separated, are scraped with a wiry-edged knife till sufficiently thin, and are then rubbed with a woollen cloth dipped in charcoal dust and water, then with rotten stone, and lastly polished with horn shavings.

The horn may be dyed by boiling it in infusions of various colored ingredients. A rich red brown color is given to it by a mixture of quicklime, pearlash, and litharge which has been boiled half an hour in water with the addition of a little pulverized dragon's blood. The compound is applied hot wherever the color is wanted, and a deeper tinge is given by renewing the application.