The basilar membrane is present between

The correct answer is scala media and scala tympani.

Step-by-Step Explanation:

The cochlea of the internal ear is a spiral-shaped, fluid-filled structure that is divided into three parallel, fluid-filled channels (or ducts) by membranes. These three channels are:
1. Scala vestibuli (the upper channel)
2. Scala media (the middle channel, also known as the cochlear duct)
3. Scala tympani (the lower channel)

These channels are partitioned from one another by two main membranes:
- The Reissner's membrane (vestibular membrane) is situated between the scala vestibuli and the scala media.
- The basilar membrane is situated between the scala media and the scala tympani.

Therefore, the basilar membrane forms the floor of the scala media (cochlear duct) and separates it from the scala tympani lying below it. This structural arrangement is crucial for hearing, as the basilar membrane supports the organ of Corti, which contains the auditory receptor hair cells.