Horn (anatomy)
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{{otheruses|Horn}}
[[Image:Goat with spiral horns.jpg|thumb|250px|A [[goat]] with spiral horns]]
A '''horn''' is a pointed projection of the [[skin]] on the head of various [[mammal]]s, consisting of a covering of '''horn''' ([[keratin]] and other [[protein]]s) surrounding a core of living [[bone]]. True horns are found only among the [[ruminant]] [[artiodactyl]]s,{{Fact|date=December 2007}} in the families [[Antilocapridae]] ([[pronghorn]]) and [[Bovidae]] ([[cattle]], [[goat]]s, [[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 [[Antilocapridae|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 [[spur]]s, [[claw]]s or [[hoof]]s.
==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]]: [[Giraffe]]s 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 [[antler]]s, 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 [[rhinoceros]]es 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 lizard]]s (''Phrynosoma''): These lizards have horns on their heads which have a hard keratin covering over a bony core, like mammalian horns.
* [[Monodontidae]]: Male [[narwhal]]s 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 beetle]]s) have horn-like structures on the head or [[thorax]] (or both). These are pointed outgrowths of the hard [[chitin]]ous [[exoskeleton]]. Some (such as [[stag beetle]]s) have greatly enlarged jaws, also made of chitin.
Many mammal species in various families have [[tusk]]s, 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 Boar]]s), [[Proboscidea]] ([[Elephant]]s), [[Monodontidae]] ([[Narwhal]]s) and [[Odobenidae]] ([[Walrus]]es).
[[Polled livestock|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 (animal)|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]].
[[Image:The three-horned one again.jpg|thumb|250px|A [[ram]] with three horns]]
==Human uses of horns==
Use of animal horns is controversial, especially if the animal was specifically hunted for the horn as a [[hunting]] [[trophy (disambiguation)|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 instrument]]s, for example the [[shofar]]. These have evolved into [[brass instrument]]s in which, unlike the [[trumpet]], the bore gradually increases in width through most of its length — that is to say, it is [[Cone (geometry)|conical]] rather than [[cylinder (geometry)|cylindrical]]. These are called [[horn (instrument)|horn]]s, though made of [[metal]].
[[Drinking horn]]s' are bovid horns removed from the bone core, cleaned and polished and used as [[drinking vessel]]s. (See also the legend of the ''Horn of plenty'', or ''[[Cornucopia]]'').
[[Black powder#History|Powder horn]]s 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]].
[[Composite bow|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" [[button]]s are usually made from deer antlers, not true horn.
==See also==
* [[Horn]] (disambiguation page)
* [[Horn (instrument)]]
* [[Horned helmet]]
* [[Polled livestock]]
* [[Tortoiseshell]]
==External links==
*[http://www.ancientmusic.co.uk/ancientinstruments/Blowing_Horns.html A site with information about the history of the cow horn as a musical instrument.]
[[Category:Animal anatomy]]
[[Category:Animal products]]
[[Category:Dinosaur anatomy]]
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