Morphology of the membrana limitans.

The morphology of the membrana limitans (ML) was studied by light and electron microscopy to further understand its functional significance. The ML is a porous shield composed of a few to several layers of tightly packed fibrocytes that separate the perilymphatic space of the cochlea and saccule from that of the utricle and canal system. These fibrocytes are thinner on the side of the vestibule. They show many desmosomes and gap junctions and are interspersed with fibrils. The 3-dimensional reconstruction from celloidin sections shows that the ML, as it is viewed from the anterior side, is rectangular in shape, with various surface curvatures and an invagination toward the internal aperture of the vestibular aqueduct. Horseradish peroxidase, a tracer substance, placed on either side of the ML fails to pass to the opposite side. The ML and trabecular meshwork may be a factor contributing to differential sensitivity of cochlear and vestibular sensory cells in the presence of noxious substances.