The cochlea (latin: cochlea) is a bony canal within the internal ear that forms a spiral shape, making 2.5 turns around its axis. The cochlea is the part of the bony labyrinth that encloses the cochlear duct of the membranous labyrinth that is involved in the sense of hearing.
The cochlea lies in front and medially of the vestibule. The cochlea has an apex that is oriented anteroinferiorly and laterally and a base that is pointing approximately in the direction of the internal acoustic meatus.
The spiral canal of the cochlea is divided into three canals by the bony spiral lamina and the basilar membrane on one side and the vestibular wall of the cochlear duct on the other side. These three canals are known as scala vestibuli, scala media and scala tympani. The confluence between the scala vestibuli and scala tympani at the apex of the cochlea is known as the helicotrema. The helicotrema forms because the bony spiral lamina and the cochlear duct end before reaching the apex of the cochlea.
The conical axis of the cochlea is called the modiolus, which also forms the medial wall of the spiral canal. It is hollowed out for housing the cochlear nerve (CN VIII).