The external ear, middle ear, and internal ear all develop from thickenings and pouches of ectoderm and mesoderm that form early in embryonic development. The external ear develops from six hillocks that fuse to form the auricle, while the external auditory meatus develops from the first pharyngeal cleft. The middle ear forms from the first pharyngeal pouch and cleft, and contains the tympanic cavity and three ossicles that develop from cartilage. The internal ear forms from the otic placode and vesicle, which give rise to the membranous labyrinth and its sensory structures for hearing and balance.

1. Development of Ear
Dr. Prabhakar Yadav
Assistant Professor
Department of Human Anatomy
B.P. Koirala Institute of Health

5. External Ear
1. External auditory meatus:
Develops from dorsal part of First pharyngeal cleft.
• First pharyngeal cleft gets filled with ectodermal
cells forming meatal plug- derived from lining
ectodermal epithelium of the first pharyngeal cleft.
• Meatal plug gets canalized at birth to form external
auditory meatus

6. Auricle or pinna:
• Develops from 6 mesodermal thickenings - auricular hillocks/ tubercles) around first pharyngeal cleft,
3 along caudal border of mandibular arch; 3 along cephalic border of hyoid arch.
• These hillocks fuse with one another to contribute in the formation of auricle of the ear.

7. Tragus, crus of helix & helix are derived from auricular hillocks of the mandibular arch
Antitragus, Antihelix,& ear lobule are derived from auricular hillocks of the hyoid arch
Mandibular arch forms only the tragus & a small area around it, rest of auricle is formed by hyoid arch.
This is consistent with the fact that auricular mucsles are supplied by facial nerve.

8. Tympanic Membrane:
Develops by apposition of tubotympanic recess of
1st pharyngeal pouch & 1st pharyngeal cleft.
1. Outer cuticular layer- derived from ectodermal
lining of first pharyngeal cleft.
2. Inner endodermal layer - derived from
endodermal lining of first pharyngeal pouch.
3. Intermediate fibrous layer- derived from
intervening mesoderm between the 1st pharyngeal
cleft and 1st pharyngeal pouch.
• Handle of malleus & chorda tympani nerve
extends into the tympanic membrane between its
intermediate fibrous layer & inner endodermal
layer.

9. Middle Ear:
1. Tympanic cavity- Distal part of tubotympanic
recess- part of first pharyngeal pouch with
contribution from second pharyngeal pouch.
• Mastoid antrum & mastoid air cells are formed by
extensions of the tympanic cavity.
• Mastoid antrum is almost of adult size at birth;
• Mastoid air cells are absent at birth;
develops by age of 2 yrs

10. 2. Ear ossicles:
(a) Malleus & incus develop from Meckel’s cartilage
(b) Stapes develops from Reichert’s cartilage
• Ossicles fully ossify in the 4th month of IUL
ie. Ossicles are first bone to Ossify.
(Ossicles at first lie outside the mucus membrane of
developing middle ear later they invaginate the mucus
membrane.)

11. Muscles:
Tensor tympanic muscle:
• Attached to Upper part of handle of malleus
• Develops from mesoderm of 1st pharyngeal
arch; supplied by mandibular nerve.
Stapedius muscle:
• Attached to stapes
• Develops from mesoderm of second
pharyngeal arch; supplied by facial nerve.

12. Pharyngotympanic Tube (Auditory tube/Eustachian tube):
Derived from narrow proximal part of tubotympanic recess.
- Connects tympanic cavity with nasopharynx

14. Internal Ear: is first of the three parts of the ear to develop.
• 4th weak of IUL, surface ectoderm on either side of myelencephalon shows a localized thickening - otic
placode.
• Otic placode- invaginates the underlying mesoderm - otic pit.
• Margins of the otic pit approach each other & fuse- Otic vesicle - that gets separated from the surface.
• Otic vesicle is primordium of the membranous labyrinth – forms its various parts.

15. Otic vesicle is at first an oval structure divides into:
Ventral saccular portion & Dorsal utricular portion.
By differential growth of its wall it give rise to
structures of Membranous Labyrinth
1. Saccular portion- saccule, cochlear duct & spiral
ganglion of vestibulocochlear nerve.
2. Utricular portion- utricle, semicircular ducts,
endolymphatic duct and sac, & vestibular ganglion of
vestibulocochlear nerve.

16. Cochlear Duct:
During 6th week, saccule forms diverticulum—cochlear duct -grows in a spiral fashion till it completes
two & half turns.
Later its connection with the saccule becomes narrow forming- ductus reuniens.

17.  Localized areas of epithelium of membranous labyrinth
undergo differentiation to form
sensory end organ of hearing & equilibrium:
• Cristae of semicircular ducts
• Macule of utricle and saccule
• Organ of corti of cochlea.

18. • Organs for hearing & equilibrium- are innervated by vestibulocochlear nerve

20. • Bony labyrinth- formed by mesenchyme surrounding membranous labyrinth.
• Mesenchyme condense to form Otic capsule which is converted into cartilage
• Between the cartilage & membranous labyrinth there is
loose periotic tissue.
• Space of the bony labyrinth is created by disappearance of periotic
tissue forming periotic space which is filled with Perilymph
• Membranous labyrinth is filled with Endolymph

21. Periotic tissue around the utricle & saccule disappears to form – Vestibule
Periotic tissue around the semicircular duct disappears to form – Semicircular canal

22. Mesenchyme of bony labyrinth forms two periotic
(perilymphatic) spaces around the cochlear duct
● Scala vestibuli above the duct
● Scala tympani below the duct.

23. Scala vestibuli is separated from the duct by vestibular membrane (Reissner’s membrane)
Scala tympani is separated from the duct by basilar membrane.
Scala Vestibuli: Communicates with vestibule
Scala Tympani: grow towards the tympanic cavity form which it remain separated by membrane

25. Congenital anomalies of external ear
1. Anotia: due to failure of mesenchymal proliferation to form auricular hillocks.
2. Preauricular appendages and pits:
preauricular appendages - due to development of accessory hillocks.
preauricular pits- due to abnormal development of auricular hillocks.
3. Atresia of external auditory meatus: due to failure of meatal plug to canalize.

26.  Anomalies of Middle ear:
• Osssicles may be malformed: abnormal fusion with one another
fusion to wall of middle ear
• Facial nerve may bulge into the middle ear and may follow
abnormal course
 Anamolies of internal ear:
• Various parts of membranous labyrinth may remain
underdeveloped

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