Submicroscopic details of the human tympanic membrane were studied utilizing a transmission electron microscope (T. E. M.) and a scanning electron microscope (S. E. M.) Three layers were distinctly recognized; outer epidermal, middle lamina propria and inner mucous layer. In pars flaccida, the middle lamina propria is formed of loose connective tissues with abundant elastic and collagen fibers. On the other hand, in the pars tensa, the middle lamina propria is formed of outer radial and inner circular fibers. Besides these two types of fibers, parabolic fibers were observed between the radial and circular fibers. The fibrils of the para tensa fibers are rectangular in cross-sectional view and are mixed with varying amounts of collagen fibrils. As in animals, the human pars flaccida was considerably thicker than the pars tensa, contrary to the popular concept that they are thinner.
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