TY - CHAP M1 - Book, Section TI - Chapter 89. Biology of Nails and Nail Disorders A1 - Tosti, Antonella A1 - Piraccini, Bianca Maria A2 - Goldsmith, Lowell A. A2 - Katz, Stephen I. A2 - Gilchrest, Barbara A. A2 - Paller, Amy S. A2 - Leffell, David J. A2 - Wolff, Klaus Y1 - 2012 N1 - T2 - Fitzpatrick's Dermatology in General Medicine, 8e AB - The nail apparatus consists of a horny “dead” product, the nail plate, and four specialized epithelia: (1) the proximal nail fold, (2) the nail matrix, (3) the nail bed, and (4) the hyponychium (Fig. 89-1A). The nail apparatus develops during the 9th embryonic week from the epidermis of the dorsal tip of the digit as a rectangular area, the nail fold that is delineated by a continuous groove.1 The proximal border of the nail fold extends downward and proximally into the dermis to form the nail matrix primordium. By the 15th week the nail matrix is completely developed and starts to produce the nail plate, which will continue to grow until death. The nail apparatus lies immediately above the periosteum of the distal phalanx. The intimate anatomic relationship between the nail and the bone is responsible for the common occurrence of bone alterations in nail disorders and vice versa. The shape of the distal phalangeal bone also determines the shape and the transverse curvature of the nail. SN - PB - The McGraw-Hill Companies CY - New York, NY Y2 - 2024/04/25 UR - accessmedicine.mhmedical.com/content.aspx?aid=56050454 ER -