:Basilar membrane:

Pronunciation GB: ˈbæzɪlə, GA: ˈbæzɪlər

A membrane which runs along the centre of the cochlea in the inner ear and forms the base of the organ of Corti. The basilar membrane vibrates in response to the different frequencies of an incoming sound. Its vibration stimulates the hair cells in the organ of Corti.

A section through the cochlea
From Borden G.J. & Harris K.S (1980) Speech Science Primer. Baltimore: Williams & Wilkins.