ABSTRACT
The development of the human nail starts at around the ninth gestational week. The nail plate is the terminally differentiated structure formed by the germinative matrix. The nail apparatus is assumed to share part of its embryonal and evolutionary origin as well as many structural and functional features with the hair follicle. Virtually all macroscopically different parts of the nail apparatus have their characteristic microscopic appearance, which may vary in disease. Merkel cells were found in the adult nail matrix and in infantile accessory digits, but others could not confirm these findings. Melanocytes are much less numerous in the nail bed or not even demonstrable with immunohistochemical techniques. Some drugs, particularly antifungal azoles, are "keratinophilic" and concentrate in the stratum corneum and the nail compared to blood and tissue values. The entire nail apparatus is fixed to the underlying terminal phalanx, the size and shape of which greatly determine those of the nail organ.
