The ear has intimate anatomical relations with various other parts, and in its diseases it is frequently associated with these parts. It is continuous externally with the skin; it is in communication by means of the Eustachian tube with the mucous membrane of the nasopharynx; it is intimately related to the bones of the skull and to the dura mater and brain. For purposes of description the diseases of the ear are divided into those of the external, middle, and internal ears, but these parts being closely related in position are frequently affected by disease together.