Anomalies of the epidermis and its appendages, due to faulty evolution of the epiblastic layer of the blastoderm, are numerous. In the nosology of dermatology such conditions are found among the hypertrophies, atrophies, new growths and affections of the appendages. The congenital keratodermas, the ectodermal nevi, and the more or less circumscribed ectodermal aplasias, are considered by many to represent abnormalities which may be traced to faulty epiblastic development. Among these conditions are found pure types and combinations: some are common; others are uncommon; some are rare. The term ectodermal defect, as used in the literature, has been employed to signify the incomplete development of the epidermis or its appendages; or its absence in circumscribed areas. Under this term, therefore, the keratodermas and the nevi may be disregarded. Congenital atrichosis, localized, generalized, and even universal, with and without deformation of the nails and teeth, is common. It is accompanied at