A mid modiolar section of a human cochlea.

A mid modiolar section of a human cochlea.

Description : The cochlea resembles a snail shell, enclosing a central canal 30 mm long which spirals for 2 1/4 turns around a central pillar, the modiolus.

The basal turn of the cochlea forms the promontory of the medial wall of the middle ear.

The osseous spiral lamina winds around the modiolus like a screw thread and separates the cochlear canal into the scala vestibuli (running from the oval window) and the scala tympani (running to the round window).

These two compartments are filled with perilymph and communicate with each other through the helicotrema, a small hole in the osseous spiral lamina near the apex of the cochlea.

The three turns of the cochlea-the apical (A), the middle (M), and the basal (13)-can be seen.

The helicotrema (H), through which the scala vestibuli and scala tympani communicate, is seen in the apical turn.

The spiral ganglion cells (SG) are located within the middle of the cochlea or modiolus.

The internal auditory meatus (IM) is located at the base of the cochlea.

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