Stratified squamous epithelium in relation to the tympanic membrane: its development and kinetics.

The pathways of auditory epithelial migration on the human tympanic membrane and their rate of movement were investigated by Hopkins rod photography of dye markings. The origin of these pathways was determined in both the human and the mouse by studying the development of the stratified squamous epithelium of the tympanic membrane and external auditory meatus from earliest embryonic life to maturity. Two pathways of migration are present. In one, epithelium moves from the region covering the tip of the handle of the malleus upwards to the lateral process and then posterior-superiorly with all dye on the pars flaccida to its posterior superior edge. In the second, dye moves centrifugally and radially outwards from the edges of the handle and pars flaccida regions to the annulus. Rate of movement can be determined approximately only and by reference to anatomical landmarks. The first pathway was traced embryologically to migration possibly commencing in the fundus of the primordial first branchial groove. The second pathway has its source in the growth of the meatal plate. A study of the development of the early meatal plate in the mouse suggests that movement of epithelium over the pars tensa region could be the result of a "pulling" effect of mitotically active cells in a generation center at the edge of the tympanic membrane resulting from negative contact inhibition.