Scanning electron microscopic studies of the capillaries crossing the scala tympani.

Scanning electron microscopic examinations were carried out on the perilymphatic space bordering the round window in guinea pigs. A number of small vessels were found crossing free through the lumen of the scala tympani in this area. The larger number (5-10) of these capillaries are suspended between the bony cochlear wall and the terminal net of fibrocytes which covers the cochlear opening of the cochlear aqueduct and spreads onto the basal third of the round window membrane. Other capillaries (3-5) cross the lumen of the scala tympani from the outer cochlear wall to the modiolus. All of these capillaries have a thin endothelium and a very thin pericytic covering. These findings suggest that the capillaries crossing the perilymphatic space may give rise to a different chemical composition of the perilymph bordering the round window in comparison with the more upper parts of the scala tympani.