The nail sinus (sinus unguis) is the place the nail root is; i.e. the bottom of the nail underneath the pores and skin. It originates from the actively growing tissue under, the matrix.
The growing a part of the nail is under the skin on the nail's proximal finish underneath the epidermis, which is the only residing a part of a nail. The hyponychium is the area of epithelium, significantly the thickened portion, underlying the free edge of the nail plate. It is sometimes known as the fast as in the phrase 'cutting to the quick'.