File:Arey1924 fig230.jpg
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Fig. 230. The development of the human nail
(Kollman)
A, 10 weeks (X 20); B, 14 weeks (X 1,3); C, longitudinal section at 14 weeks (X 24).
Nails are modifications of the epidermis that correspond to the claws and hoofs of lower mammals. The nail anlage is recognizable in fetuses of 10 weeks as an epidermal, pouch-like fold that soon extends from the proximal border of the future exposed plate almost to the articulation of the terminal phalanx (Fig. 230 C) this proximal nail fold also continues laterally on either side as the lateral nail folds (Fig. 230 A, B).
The material of the nail is developed in the lower lamina of the proximal nail fold (Fig. 230 C). Certain of the epidermal cells, which, according to Bowen, represent a modified stratum lucidum, develop keratin fibrils during the fifth fetal month. These appear without the preliminary keratohyalin stage, as is the case in ordinary epidermis. The cells flatten and form the compact mass of which the nail plate is composed. Thus, the nail substance differentiates in the proximal nail fold as far distad as the outer edge of the Iunula (the whitish crescent at the base of the adult nail). Beyond the lunule, the underlying epidermis takes no active part in development. The stratum corneum and periderm of the epidermis for a time cover completely the free nail and are termed the eponychium (Fig. 230 C).
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Reference
Arey LB. Developmental Anatomy. (1924) W.B. Saunders Company, Philadelphia.
Cite this page: Hill, M.A. (2024, April 24) Embryology Arey1924 fig230.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Arey1924_fig230.jpg
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
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