promontory of tympanic cavity

 The promontory of the tympanic cavity,

 also known as the cochlear promontory is a rounded hollow prominence, formed by the projection outward of the first turn of the cochlea.

It is placed between the oval window and the round window 

its surface contains small grooves to lodge branches of the tympanic plexus.

A spicule of bone frequently connects the promontory to the pyramidal eminence.

the first bend of the facial nerve (genu) is found here