Incudal folds and epitympanic aeration.

Thirty-seven temporal bones were dissected, and the posterior tympanic and epitympanic folds recorded and photographed. Histologic details were documented from four serially sectioned temporal bones, two normal and two inflamed. Of these 41 specimens, 31 were normal, and 10 showed signs of inflammation. The type for the lateral fold was incudomalleal in 16 and incudal in 25 ears. Incus intercrural and incudostapedial folds appeared only exceptionally. Medial and superior incudal folds were not present in normal ears. The anterior tympanic isthmus was a constant, large aeration pathway. In chronically inflamed ears, its partial or total block was caused by polypoid or large sheet-like folds. Inactive sequelae appeared as mature, simple, one-layer or extensive multilayer networks of webs, connected with a deeply indrawn incudomalleal fold. The small posterior isthmus was open to the incudal fossa in 13 ears, and in 28, it was sealed off by a posterior incudal fold. The mastoid air cell tracks were (in ten of 37 dissected ears) open to the incudal fossa, or directly, to the posterior tympanum. Auxiliary pathways due to membrane defects were found in both the horizontal and descending portions of the incudomalleal fold. Excepting the chordal, incudomalleal, and posterior incudal folds, fold-like webs in the posterior tympanum and epitympanum are of inflammatory origin.