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horny formations at the ends of the digits of terrestrial vertebrates. In amphibians the claws are thickenings of the horny layer of the epidermis.
True claws are found on the majority of reptiles, all birds, and many mammals; they are used as auxiliary organs during ambulation and as weapons in active defense and attack. Claws are usually horny covers on the ends of the phalanxes of the fingers and toes; the upper side is formed from a hard cornaceous substance (claw layer), and the underside (cushion layer) is soft. The unequal wear of the two layers keeps the claws sharpened.
Claws in mammals are particularly varied: they are sharp and powerful in climbing animals, relatively thin and retractable in felines (weapons of attack), and large and thick in burrowing animals. In swimming animals claws have partially or completely disappeared. In mammals nails and hooves are variations of claws.