The Tympanic Membrane - Dimensions: Its dimensions are: 9-10 mm height and 8-9 mm width. It is 0.1 mm thick. Position: Tympanic membrane (TM) is a paition wall between the EAC and the middle ear. It is positioned obliquely. It forms angle of 55deg with deep EAC. Structure: Tympanic membrane consists of the following three layers: Outer epithelial layer: It is continuous with the EAC skin. Middle fibrous layer: The middle layer is made up of fibrous tissue, which is lined on the outside by skin (continuous with that of the external acoustic meatus), and on the inside by mucous membrane of the tympanic cavity. The fibrous layer contains collagen fibres and some elastic fibres. The fibres are arranged in two layers. In the outer layer they are placed radially, while in the inner layer they run circularly. Inner mucosal layer: The mucous membrane is lined by an epithelium which may be cuboidal or squamous. It is said that the mucosa over the upper pa of the tympanic membrane may have patches of ciliated columnar epithelium, but this is not borne out by EM studies. Otoscopy: Normal tympanic membrane is shiny and pearly-grey in colour. Its trans parency varies from person to person. REF : Inderbir Singh's Textbook of Human Histology, Seventh edition, pg.no., 413.