horn, in zoology, one of a pair of structures projecting from the head of a hoofed animal, used chiefly as a weapon. In cattle, sheep, Old World antelopes, and related animals the horns are permanent and unbranched and are usually present in both sexes. They are composed of a sheath of keratin—a tough fibrous material derived from epithelial tissue—overlying a bony core projecting from the skull. In the deer family the branched structures, called antlers, are composed entirely of bone with no actual horn substance; they are usually present only in the male and are shed annually. The horns of the pronghorn have characteristics of both true horns and antlers. Rhinoceros horns are not true horn but greatly modified hair, derived entirely from the epidermis. Horns have long been used for many purposes, e.g., drinking cups, spoons, trumpets, containers for gunpowder, and combs. Carved pieces of horn have been found dating from prehistoric times. In art and religion horns symbolize power. The "horns of the altar" (Amos 3.14) symbolized divine protection. Hornlike protuberances appear on other animals, e.g., on the horned toad and the horned pout.