The nails are appendages of the skin. Each nail has a hard outer crust protecting it, and inside there is a blood and nerve supply. Nails, be in organs of defense and aids in locomotion, as well as being useful in holding food while the teeth tear it apart, are strongly attached to the toes - much more so than our nails.
Dogs' nails are constantly growing to make up for the loss of nail which, in a wild dog, would be worn off by contact wills rough surfaces. House pets seldom have the opportunity of wearing down the nails sufficiently. Dogs running the streets keep their nails filed off by the pavements, but dogs walking on carpets or sleeping most of the time having no such opportunity and often their nails curve back under the foot until they press into the toes. Various dogs differ markedly in their rate of nail growth. In some the rate of growth is so rapid that even running on city streets fails to wear their nails off.
