Guinea pig tectorial membrane profile in an in vitro cochlear preparation.

The guinea pig cochlea was examined under high-magnification light microscopy in an in vitro preparation. After extraction of the otic capsule, the bulla was opened widely and a small hole made into the fourth turn of the scala vestibuli. The organ of Corti was visualized under artificial endolymph at 600 X magnification. Added 1-micron titanium dioxide particles settled on the upper surface of the transparent tectorial membrane. Particle positions showed that much of this upper surface lay in a flat sheet that extended centrifugally almost to the Hensen's cells, giving the impression it was attached there. The sheet extended at least to the level of the inner hair cells, where a tectorial membrane thickness of about 40 micron was reached. Titanium dioxide particles were seen regularly in immediate proximity to the hair cell cilia, indicating that scala media is continuous with the subtectorial space. Upon mechanical manipulation, Hensen's cells proved to be extremely cohesive and elastic. It is suggested that hair cell stereocilia provide major mechanical connections for the tectorial membrane.