Horn (anatomy)

A horn is a pointed projection of the skin on the head of various mammals, consisting of a covering of horn (keratin and other proteins) surrounding a core of living bone. True horns are found only among the ruminant artiodactyls, in the families Antilocapridae (pronghorn) and Bovidae (cattle, goats, antelope etc.). These animals have one or occasionally two pairs of horns, which usually have a curved or spiral shape, often with ridges or fluting. In many species only the males have horns. Horns start to grow soon after birth, and continue to grow throughout the life of the animal (except in pronghorns, which shed the outer layer annually, but retain the bony core). Similar growths on other parts of the body are not usually called horns, but spurs, claws or hoofs.

Other hornlike growths
The term "horn" is also popularly applied to other hard and pointed features attached to the head of animals in various other families:
 * Giraffidae: Giraffes have one or more pairs of bony bumps on their heads. These are covered with furred skin, and although they look as if they ought to have horns on them, they do not.
 * Cervidae: Most deer have antlers, which are not true horns. When fully developed antlers are dead bone without a horn or skin covering; they are borne only by adults (usually males) and are shed and regrown each year.
 * Rhinocerotidae: The "horns" of rhinoceroses are made of keratin and grow continuously, but do not have a bone core.
 * Ceratopsidae: The "horns" of the Triceratops were extensions of its skull bones although debate exists over whether they had a keratin covering.
 * Horned lizards (Phrynosoma): These lizards have horns on their heads which have a hard keratin covering over a bony core, like mammalian horns.
 * Monodontidae: Male narwhals have a single long tusk, a modified tooth, which looks like a horn, and is twisted like that of the fictional unicorn.
 * Insects: Some insects (such as rhinoceros beetles) have horn-like structures on the head or thorax (or both). These are pointed outgrowths of the hard chitinous exoskeleton.  Some (such as stag beetles) have greatly enlarged jaws, also made of chitin.

Many mammal species in various families have tusks, which often serve the same functions as true horns, but are in fact oversize teeth. These include the Moschidae (Musk deer, which are ruminants), Suidae (Wild Boars), Proboscidea (Elephants), Monodontidae (Narwhals) and Odobenidae (Walruses).

polled animals or pollards are those of normally-horned (mainly domesticated) species whose horns have been removed, or which have not grown. In some cases such animals have small horny growths in the skin where their horns would be – these are known as scurs.

Animal uses of horns
Animals have a variety of uses for horns and antlers, including defending themselves from predators and fighting members of their own species for territory, dominance or mating priority. In addition, horns may be used to root in the soil or strip bark from trees. In animal courtship many use horns in displays. For example, the male blue wildebeest reams the bark and branches of trees to impress the female and lure her into his territory. Some animals with true horns use them for cooling, the blood vessels in the bony core allowing the horns to function as a radiator.

Human uses of horns
Use of animal horns is controversial, especially if the animal was specifically hunted for the horn as a hunting trophy or object of decoration or utility. Some animals are threatened or endangered to reduced populations partially from pressures of such hunting.

Some peoples use bovid horns as musical instruments, for example the shofar. These have evolved into brass instruments in which, unlike the trumpet, the bore gradually increases in width through most of its length &mdash; that is to say, it is conical rather than cylindrical. These are called horns, though made of metal.

Drinking horns' are bovid horns removed from the bone core, cleaned and polished and used as drinking vessels. (See also the legend of the Horn of plenty, or Cornucopia).

Powder horns were originally bovid horns fitted with lids and carrying straps, used to carry gunpowder. Powder flasks of any material may be referred to as powder horns.

Antelope horns are used in traditional Chinese medicine.

Horn can also refer to keratin, the material of which a horn is made, sometimes including keratin from other parts of animals, such as hoofs. Horn may be used as a material in tools, furniture and decoration, among other uses. In these applications, horn is valued for its hardness, and it has given rise to the expression hard as horn. Horn is somewhat thermoplastic and (like tortoiseshell) was formerly used for many purposes where plastic would now be used. Horn may be used to make glue.

Horn bows are bows made from a combination of horn, sinew and usually wood. These materials allow more energy to be stored in a short bow than wood would.

Ivory comes from the teeth of animals, not horns.

"Horn" buttons are usually made from deer antlers, not true horn.