Hair
Hair, collective term for slender, threadlike outgrowths of the epidermis of mammals, forming a characteristic body covering. No animals other than mammals have true hair, and all mammals have hair. Even such apparently hairless mammals as the rhinoceros, elephant, and armadillo have hairs around the snout, at the tip of the tail, and behind each scale, respectively. (Whales and manatees have hair only in the embryonic state.) When the individual hairs are fine and closely spaced, the coat of hair is called fur; when soft, kinked, and matted together, the coat is called wool. Coarse, stiff hairs are called bristles. When bristles are also pointed, as in the hedgehog and porcupine, they are called spines or quills. In humans the development of the hair begins in the embryo, and by the sixth month the fetus is covered by a growth of fine hair, the lanugo. In the first few months of infancy the lanugo is shed and is replaced by hair, relatively coarse over the cranium and the eyebrows, bu...