Development of the Ear

A. External ear

• Pharyngeal groove 1 forms the external auditory meatus and tympanic membrane.
• Auricular hillocks form the auricle.

B. Middle ear

• Pharyngeal arch 1 forms the incus, malleus, tensor tympani muscle, and trigeminal nerve.
• Pharyngeal arch 2 forms the stapes, stapedius muscle, and facial nerve.
• Pharyngeal pouch 1 forms the auditory tube and middle ear cavity.
• Pharyngeal membrane 1 forms the tympanic membrane.

C. Internal ear

• Develops from the otic placodes (thickening of embryonic ectoderm), which invaginate to form the otic or auditory vesicles (otocysts).
• Auditory vesicle (otocyst) is the primordium of the internal ear and is derived from the surface ectoderm.
• Utricular portion forms the utricle, semicircular ducts, and vestibular ganglion of CN
• Saccular portion forms the saccule, cochlear duct, and spiral ganglion of CN VIII.
• Vestibular pouch forms the semicircular canals, the utricle, and endolymphatic duct.
• Cochlear pouch gives rise to the saccule, which forms a diverticulum that, in turn, forms the cochlear duct.
• Otic capsule develops from the mesenchyme around the otocyst and forms the perilymphatic space, which develops into the scala tympani and scala vestibule. The cartilaginous otic capsule ossifies to form the bony labyrinth.
  

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