The perilymph, present in the scala vestibule and scala tympani, drains into the CSF through the

The perilymphatic chamber of the vestibular system has a wide connection to scala vestibuli, which in turn connects to scala tympani by an opening called the helicotrema at the apex of the cochlea. Scala tympani is then connected to the cerebrospinal fluid (CSF) of the subarachnoid space by the cochlear aqueduct. ref - BD chaurasia 6e vol3 pg