Fig. 2. Anatomy of the adult mammalian cochlea. (A) Cross-section through the human head, illustrating the position of the inner ear. The ear has three parts: the external ear, which consists of the pinna and external auditory meatus (EAM) and ends at the tympanic membrane (TM, green); the middle ear (ME, orange), which contains the three middle ear bones; and the inner ear, which includes the bony labyrinth (BL, light blue) and the statoacoustic ganglion (SAG, purple). (B) Lateral view of the mouse inner ear (boxed region in A) with sensory epithelia in green. LC, lateral semicircular canal; SC, superior semicircular canal; PC, posterior semicircular canal; Sac, saccule; Utr, utricle; Coch, cochlea; ES, endolymphatic sac. The endolymphatic duct is hidden from view but connects the ES to the semicircular canals. (C) Cross-section through the boxed region in B, illustrating the anatomy of the cochlear duct. The duct is separated into scala vestibule (SV), scala media (SM) and scala tympani (ST). The sensory epithelium of the cochlea, the organ of Corti (boxed), is located on the floor of the scala media. (D) Cross-section of the organ of Corti, containing a single inner hair cell (I, green), three outer hair cells (1-3, green) and non-sensory supporting cells (blue), which include the pillar cells (purple). Inner and outer sensory hair cells are separated by the tunnel of Corti (TC), a fluid filled structure that is bounded by inner and outer pillar cells (IP and OP, purple).