<P> The lunula ("small moon") is the visible part of the matrix, the whitish crescent - shaped base of the visible nail . The lunula can best be seen in the thumb and may not be visible in the little finger . </P> <P> The nail bed is the skin beneath the nail plate . Like all skin, it is made of two types of tissues: the deeper dermis, the living tissue which includes capillaries and glands, and the epidermis, the layer just beneath the nail plate, which moves toward the finger tip with the plate . The epidermis is attached to the dermis by tiny longitudinal "grooves" called matrix crests (cristae matricis unguis). In old age, the nail plate becomes thinner, and these grooves become more visible . </P> <P> The nail sinus (sinus unguis) is where the nail root is; i.e. the base of the nail underneath the skin . It originates from the actively growing tissue below, the matrix . </P> <P> The nail plate (corpus unguis) is the hard part of the nail, made of translucent keratin protein . Several layers of dead, compacted cells cause the nail to be strong but flexible . Its (transverse) shape is determined by the form of the underlying bone . In common usage, the word nail often refers to this part only . </P>

Describe the structure and functions of the nail and skin