From an embryologic point of view, certain diseases of the oral and nasal mucosa are logically related to those on the cutaneous surface. A common ectodermic origin brings affections of these structures in closer relation to each other than with the diseases of the deeper digestive tract which originates from the entoderm. Furthermore, eruptions of the oral cavity are objectively demonstrable, and not infrequently they are a part of the clinical picture of a cutaneous eruption. Specialties in medicine frequently overlap, and borderline conditions are encountered which may pertain to general medicine, surgery or to the branch which has devoted particular attention to a certain class of affections. The implication of the mucous membranes in the acute exanthems is almost invariable. The pharyngeal congestion in scarlatina and the Koplik spots in measles aid materially in diagnosis before the skin eruption appears. To review the literature of mouth eruptions and to