This is a structural membrane in the Cochlea that seperates two fluids in the Cochlea. The membrane is slightly bonier than other parts of the cochlea like the oval window. The two fluid chemicals it separates are endolymph and the perilymph which are separated because of their different biochemical and electrical properties. Between the middle and outer ear sound waves are translated into fluid vibrations and carried in these chemicals. Before they are passed on to the hair cells for the last leg of the journey.