The nail apparatus consists of the nail plate, the nail fold, the nail matrix, the sterile matrix and the hyponychium.
The nail plate is a durable layered keratinized structure that is formed continuously with dorsal, intermediate, and ventral nail plates. It arises from the maturation and keratinization of the nail matrix and is firmly connected to the sterile matrix. The dorsal and intermediate layers of the nail plate are produced by the nail matrix, whereas the ventral layer is produced by the sterile matrix.
The sides of the nail plate are bounded by lateral nail folds that are related to the proximal fold. The lateral nail folds are cutaneous folded structures that enclose the lateral free edges of the nail plate providing the lateral borders to the nail.
The proximal ( posterior ) nail fold is a skin fold that provides the visible proximal border of the nail. On the lower portion of the undersurface, this becomes the dorsal matrix. The Eponychium refers to the upper portion of the ventral aspect of the proximal of nail fold. The cuticle is the tissue that seals the nail cul-de-sac which is formed by the dorsal and ventral side of the proximal nail fold.
The nail matrix (nail root) is a specialized epithelial structure that overlies the central portion of the distal phalanx. Keratinocytes of the nail matrix divide in the basal cell layer and keratinize above. The distal matrix is partially covered by the proximal nail fold. The convex margin of the matrix is visible through the nail plate as a white crescent-shaped area more pale than the adjacent nail bed called the lunula (half moon).
The sterile matrix epidermis, the nail bed, the vascular bed upon which the nail rests extends from the distal edge of the lunula to the hyponychium. Sterile matrix cells differentiate into the nail plate. The contribution of the sterile matrix to nail plate formation is approximately one fifth the thickness and mass of the terminal nail.
The hyponychium is the cutaneous margin under the free nail between the onychodermal band and the distal grove. The onychodermal band creates a grey line at the edge of the nail bed before the free edge of the nail plate. It represents the first barrier to penetration of materials to beneath the nail plate. The distal grove (limiting furrow) is an epidermal ridge demarcating the border between subungual structures and the toe pad.