The inner ear is derived from a pair of surface sensory placodes (otic placodes) that appear in human development during week 4 in the head region lying behind the second pharyngeal arch.

These otic placodes fold inwards forming initially a depression, then pinch off entirely from the surface forming an epithelium surrounding a fluid-filled sac or vesicle (otic vesicle, otocyst, auditory vesicle). The vesicle sinks into the head mesenchyme some of which closely surrounds the otocyst forming the otic capsule.

The otocyst finally lies close to the early developing hindbrain (rhombencephalon) and the developing vestibulo-cochlear-facial ganglion complex.

The otocyst epithelium then undergoes a series of morphological changes, forming the primitive membranous labyrinth. During the human fetal period this will differentiate into the inner ear components for hearing (cochlea) and balance (semi-circular canals). Cochlear development involving a transcription factor spatiotemporal gradient continues through to GA week 16.[1]

The adult cochlear has a "snail-shell" appearance, with the total number of turns differing between species. The adult human cochlear is typically described as having 2.5 turns, but this can vary up to 2.75 or even 3 turns.[2]

The "organ of corti" that develops within the cochlea was first identified by Alfonso Giacomo Gaspare Corti (1822–1876), an Italian ana

Reference

https://embryology.med.unsw.edu.au/embryology/index.php/Hearing_-_Inner_Ear_Development