Tympanic membrane part II. Pars flaccida

Submicroscopic morphological details of the pars flaccida (Shrapnell's membrane) of the cat, squirrel monkey, rabbit and sheep were studied. Three layers were distinctly recognized: outer epidermal, middle lamina propria and inner mucous. The epidermis was composed of three to four layers of keratinizing squamous cells, and the inner mucous layer was formed by a single-cell layer of simple squamous or cuboidal cells. These cells could accommodate cilia or secretory granules. The middle lamina propria was composed of loose connective tissue containing fibroblasts, nerve fibers and capillaries. The regularly arranged collagenous fibers which were present in pars tensa were not found. Abundant elastic fibers were found in this layer intermixed with collagenous fibers. The thickness of Shrapnell's membrane in the materials used was considerably greater than that of pars tensa.