Embryology of the Human Ear
Ashley Balaker, M.D.
March 17, 2010
Outline
• Inner Ear
• Middle Ear
• External Ear
Inner Ear
• Ectoderm = membranous labyrinth
• Mesoderm = bony labyrinth
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3rd week
Surface ectoderm = otic placode
Invaginates --> otic pit
4th week
Pit edges fuse to become otocyst
Inner Ear
• Dorsal utricular portion, ventral saccular
portion
• Utricular portion
– 3 diverticula for semicircular canals
• Saccular portion
– Tubular diverticulum (cochlear duct) grows in
spiral fashion to become membranous cochlea
– The organ of Corti differentiates from cells along
the wall of the cochlear duct.
Inner Ear
• 6th week
• neuroectoderm --> spinal and vestibular
ganglia and corresponding sensory
nerves
• Mesoderm around otocyst soon forms a
cartilaginous otic capsule.
• Ossifies by 25 weeks
Inner Ear
• Vacuoles containing the perilymph develop
within the otic capsule.
• The vacuoles enlarge and unite to form the
perilymphatic space
• Divides into the scala tympani and the scala
vestibuli.
• The cartilaginous otic capsule ossifies to form
the bony labyrinth of the inner ear
(mesoderm).
Middle Ear
• 1st pharyngeal pouch endoderm
– Lining of middle ear (tympanic cavity)
– Connection to pharynx elongates and
forms eustachian tube
Middle Ear
• 1st and 2nd pharyngeal arch cartilage
(mesoderm) --> ossicles
• 1st (Meckel’s): epitypanum ossicles
– Head of malleus, body and short process of incus
• 2nd (Reichert’s): mesotympanum ossicles
– Long process malleus, long process incus, stapes
superstructure
• Stapes footplate: otic capsule
Middle Ear
• Ossicles full sized by 15 weeks
• Ossify by 25 weeks
Middle and External Ear
External Ear
• EAC develops from the surface
ectoderm that covers the dorsal end of
the first pharyngeal grove.
• A solid epithelial plate meatal plug
develops at the bottom of the funnelshaped pharyngeal groove.
External Ear
• TM
– Inner layer endoderm
– Middle layer mesoderm
– Outer layer ectoderm
Auricle
• 6 Hillocks of His (mesoderm)
• 1st pharyngeal arch
– 1: Tragus
– 2: Helical crus
– 3: Helix
• 2nd pharyngeal arch
– 4: antihelix
– 5: antihelix
– 6: antitragus
Auricle
Thanks