The mucous membranes of 66 normal human Eustachian tubes, middle ears, and mastoid air cells were examined using the SEM, TEM and light microscopes. The density of population in the ciliated cells ranged from dense to sparse in the following areas in this order: Eustachian tube, hypotympanum, anterior of epitympanic recess, anterior and posterior parts of the promontory, peripheral part of the epitympanic membrane, posterior of epitympanic recess, prominence of the facial canal, ossicles, antrum, perifacial area in the mastoid air cell, and the rest of the mastoid air cells. The pattern of ciliated cell distribution and the fact that mucous droplets and a mucous blanket could be seen frequently on the lining of the Eustachian tube, middle ear, and mastoid air cells further support the concept that middle ear clearance is carried out by an active mucociliary system in most parts. Numbers of ciliated cells are not static but change rapidly to local demands in such situations as infection and serous effusion.
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