Nail structure and growth
A nail is a horn-like envelope covering the tips of the fingers and toes in humans, most non-human primates, and a few other mammals. Nails are similar to claws in other animals. Fingernails and toenails are made of a tough protective protein called keratin. This protein is also found in the hooves and horns of different animals. The growing part of the nail is under the skin at the nail's proximal end under the epidermis, which is the only living part of a nail. In mammals, the growth rate of nails is related to the length of the terminal phalanges.
- Evolution of nails in primates