The inner portion, called the membranous labyrinth, consists essentially of a closed membranous sac, which is filled with the endolymph.
"Physiology and Hygiene for Secondary Schools"
Francis M. Walters, A.M.
The scala media belongs to the membranous portion of the internal ear and is, therefore, filled with the endolymph.
"Physiology and Hygiene for Secondary Schools"
Francis M. Walters, A.M.
The membranous bag itself contains a similar fluid, the endolymph.
"A Practical Physiology"
Albert F. Blaisdell