Horn in Biology Overview of Structure and Function

In zoology, horn, either of the pair of hard processes, which grow from the upper portion of the head of several hoofed mammals. Also, the term is loosely applied to the antlers and to the same structures present on certain dinosaurs, lizards, birds, and insects. True horns are the simple unbranched structures, which are never shed—are found in sheep, cattle, antelopes, and goats. They consist of a core of bone, which is surrounded by a layer of horn (called keratin) that is in turn covered by the keratinized epidermis.

Pair of Horns

One pair of horns is usual; however, either two or more pairs take place in some wild species and a few domesticated breeds of sheep. Polycerate (the multi-horned type) sheep breeds include the Icelandic, Hebridean, Manx Loaghtan, Jacob, and the Navajo-Churro.

Usually, horns have a curved or spiral shape, often with fluting or ridges. In several species, only males contain horns. Horns begin to develop shortly after birth and continue to develop throughout the animal's life (except in pronghorns that annually shed the outer layer but retain the bony core). Deformed or partial horns in livestock are known as scurs. The same growths on the other parts of the body are not usually referred to as horns; however, claws, spurs, or hooves, depending on the body part on which they take place.

The below figure shows the pair of horns on a male impala.

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Horn Lengths and Configurations

The antlers of deer are not known as horns. Shed yearly, which are composed entirely of bone, though they bear a velvety epidermal covering at the time of their growth period. They increasingly become branched with their age. The rhinoceros "horn" is composed of the fused and heavily keratinized hairlike epidermis. Horns serve as the weapons of defence against predators and of an offence in battles between the males for breeding access to females.

The below picture shows horn lengths and configurations in various antelopes.

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Types of Horns

Let us discuss the types of animal horns in detail.

Bovine Horns

The only true horns present in the animal kingdom belong to the Bovidae family members, or the animals with horns names, which includes sheep, cows, antelopes, and goats. Horns protrude from the skull, and they are composed of a bony core sheathed in the keratin, a similar material, which makes up our fingernails. Horns never branch while they curl, curve, or spiral. They never either shed or stop growing. Also, horns are present on the males of all species of bovine, and usually, they are also present on the females.

Rhino Horns

While the rhino is a well-known thing for its horned nose, this is not as similar as a bovine horn. The rhino horns lack the true horns' bony core. Instead, they are completely made of keratin. And, they do contain melanin and calcium, which adds some strength and protects the horn from the UV rays of the sun. Rhino horns are the same as bird and hooves beaks.

Giraffe Horns

Giraffe horns, which are known as ossicones, share several characteristics with the bovine horns. They are paired, permanent, and do not branch. However, they are covered in both hair and skin. Female and male giraffes contain horns present from birth. Like most horned creatures, male giraffes will use their available horns when sparring with the other males.

Pronghorn Horns

While known as pronghorn antelopes, pronghorns do not belong to the Bovidae family as antelopes do. Pronghorns are the only members of their family, called Antilocapridae. Pronghorn horns are kind of like a mix of antlers and true horns. Their horns branch, containing two prongs. Also, they have keratin sheaths and bony cores, like bovine horns, but they annually shed them, similar to the antlers.

Antlers

Technically, while antlers are not horns, they are the same in several respects. Antlers are more characteristic to the members of the deer family or Cervidae family. They grow from ahead of deer, and males use them when sparring with the other males. However, unlike horns, antlers exist only in the males in most of the species. Antlers are only made of bone, but not keratin. Deer shed their antlers annually, growing a brand new set each mating season.

Some Hornlike Growths

The word "horn" is popularly applied to the other hard and pointed features, which are attached to the head of animals in other several families:

• Rhinocerotidae: The "horns" of the rhinoceroses are made of keratin, a similar substance as fingernails, and they grow continuously but do not contain a bone core.

• Giraffidae: Giraffes contain either one or more pairs of bony bumps on their heads, which are known as ossicones. These are covered with furred skin.

Several mammal species in different families have tusks, which often serve similar functions as horns, but in fact, they are oversized teeth. These are the Suidae (Wild Boars), Moschidae (Musk deer - ruminants), Monodontidae (Narwhals), Proboscidea (Elephants), and Odobenidae (Walruses).

On Humans

Cutaneous horns are the only existing examples of horns growing on the people.

Cases of the people growing horns have been described historically, at times with mythical status. However, the researchers have not discovered photographic evidence of the phenomenon. Outgrowings are found in some human cadaveric specimens, although they are classed as osteomas or other excrescences instead.