The method of formation of the human nail has been the cause of some debate. It is generally believed that the nail plate is entirely formed from the matrix and that the bed contributes little or nothing to its formation. It seems certain that this is usually true, and when one sees onycholysis with the nail plate widely separated from its bed but remaining firmly attached in the matrix area, there can be little doubt that the bed was acting only as a support before separation occurred.
Lewis1,2 put forward an alternative opinion and maintained that in most cases the nail is formed in 3 parts which he called dorsal, intermediate, and ventral nails. The intermediate nail is derived from that part of the nail organ normally considered as constituting the matrix, namely, the posterior part of the floor of the nail-fold invagination, extending as far forward as the
SAMMAN PD. The Ventral Nail. Arch Dermatol. 1961;84(6):1030–1033. doi:10.1001/archderm.1961.01580180146027
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