Cochlea

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Cochlea :

It is the main hearing organ which is connected with saccule by a short ductus reuniens leading from the saccule. It is spirally coiled that resembles a snail shell in appearance. It tapers from a broad base to an almost pointed apex.

Internally it consists of three fluid filled chambers or canals, the upper scala vestibuli, lower scala tympani, and the middle scala media (cochlear duct). Both scala vestibuli and scala tympani are filled with perilymph. However scala media is filled with endolymph. Both the scala vestibuli and scala tympani are connected with each other at the apex of the cochlea by a small canal, the helicotrema.

It is important to mention that near the base of the scala vestibuli the wall of the membranous labyrinth comes in contact with the fenestra ovalis, while at the lower end of the scala tympani lies the fenestra rotunda.