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Spur (zoology)
A spur is an outgrowth of bone covered in a sheath of horn found in various anatomical locations in some animals. Unlike claws or nails, which grow from the tip of the toes, spurs form from other parts of the foot, usually in connection with joints where the toes meet the foot or the foot meets the long bones. Spurs are most commonly found on the hindfeet, though some birds possess spurs at the leading edge of the wings.
==Anatomy==
A spur is much like a true horn; it is a bony core attached to the skeleton and has an outer horny layer. Like horns, the spur grows from the base outwards, so the tip is older than the base. Some spurs form as an outgrowth of an existing bone, though most are secondarily formed as dermal bone hinged to the skeleton through a semi-rigid joint. Spurs on the hind-feet do not appear to molt, but the wing spurs of birds are molted once a year along with the wing feathers.〔
Unlike claws, spurs are normally straight or only slightly curved, making them suited to striking or stabbing. In birds and mammals, their function appears to be for fighting, defense and territory marking, rather than for predation.〔 In reptiles, spurs are usually only found in the males and are used as holdfasts or to stimulate the female during copulation.〔Pough ''et al.'' (1992). ''Herpetology'': Third Edition. Pearson Prentice Hall:Pearson Education, Inc.〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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