Attached peripherally to the outer wall of the cochlea, the cochlear duct creates two canals (the scala vestibuli and the scala tympani), which extend throughout the cochlea and are continuous with each other at the apex through a narrow slit (the helicotrema):
The scala vestibuli is continuous with the vestibule.
The scala tympani is separated from the middle ear by the secondary tympanic membrane covering the round window (Fig. 8.131).