Found on both male and female animals in some species, horns continue growing throughout the life of particular creatures. Made of keratin, a substance making up hooves, hair and nails, horns appear as bony growths under the skin formed from connective tissue. Growing separate from the skull bone, horns become a protruding bonelike extension from the head. Animals with horns include hoofed, even-toed cattle, sheep, and goats. Unlike antlers, most horns never shed.
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Differing from true horns with a core and sheath, the rhino horn consists of skin cells and connective tissue (papilla) forming a hairlike substance material extending upward. In single-horned rhino species, the horn grows over the nasal bones, while other rhinos develop a second horn over the frontal bone. Both horns curve toward the rhino face.
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Beginning in the giraffe fetal stage, this horn develops from tough elastic tissue (cartilage). Giraffes differ from other even-toed and horned mammals because its horns do not stick out from the skull, but rather form along the connective tissue holding the frontal and parietal head bones together. The horn finally fuses to the front of the giraffe skull by age four.
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America's male and female bison or buffalo grow two horns made of a protein similar to hair. These hollow horns develop over a bonelike centre producing one layer of horn a year from the age of four. The bison horn tip (cap) remains solid, but if broken off by accident while digging in mud, the short core hardens as the horn grows outward to make a new cap.
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Big Horn Sheep
Big-coiled horns of mature male sheep (rams) might form 10 per cent of the animal's body weight. Unlike the massive male horns, the female (ewe) carries a spear-like projecting horn. The chipped or frayed horn of big horn sheep normally results from rams cracking horns in combat or from digging. Achieving the ram "full curl" horn takes 7 to 8 years from birth.
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Horns of the African buffalo reflect the sex and age of the animal. Both male and female African or Cape buffalo grow heavy-ridged horns curving upward into a hook. Male buffalo horns are longer than female horns, reaching nearly 2 feet from tip to tip. African forest buffalo form horns straight out then backwards, in line with the forehead.