Ewing,1 in discussing tumors of the hypophysis, said that cholesteatoma as well as the true dermoid containing hair and sebaceous material occasionally appears in or near the sella turcica. He intimated that it may take its origin from ectodermal rests carried in with the closure of the vesicles of the brain. In some instances such a so-called tumor may have developed by metaplasia from remnants of the hypophysial duct. Fetal implantation may account for these teratomas of the brain, in which class Ewing seems to have been inclined to place cholesteatoma found in this region. A teratoid tumor at the base of the skull is commonly referred to as buccal ectoderm misplaced in the development of the hypophysis. Ewing stated: The relation of the medullary groove to the ectoderm, the complex step in the formation of the brain and ventricles, and the formation and union of the cranial bones give