The ear develops from three parts - the external ear, middle ear, and inner ear. The external ear develops from swellings around the first pharyngeal cleft. The middle ear develops from the first pharyngeal pouch. The inner ear develops from thickenings of surface ectoderm that invaginate to form the otic vesicles. These vesicles give rise to the membranous labyrinth containing the saccule, utricle, semicircular canals and cochlear duct. The ossicles of the middle ear develop from cartilage of the pharyngeal arches. Congenital deafness and abnormalities of the external ear can result from abnormal development and are often associated with other malformations

1. EMBRYLOGY
BY
DR. THAAER MAOHAMMED DAHER ALSAAD
M.B.Ch.B. (MBBS) F.I.B.M.S. (PhD)
SPECIALIST IN GENERAL SURGERY
SENIOR LECTURER
IMS MSU

2. Ear
DEVELOPMENT

3. Ear
• In the adult, the ear forms one anatomical
unit serving both hearing and equilibrium.
• In the embryo it develops from three
distinctly different parts:
1. The external ear, the sound collecting organ;
2. The middle ear, a sound conductor from the
external to the internal ear;
3. The internal ear, which converts sound waves
into nerve impulses and registers changes in
equilibrium.

4. Scanning electron micrograph of a mouse
embryo equivalent to approximately 28 days
of human development. The otic placodes,
as shown in B, are invaginating to form the
otic pits (arrows). Arrowhead, second arch;
H, heart; star, mandibular prominence.
Region of the rhombencephalon
showing the otic placodes
in a 22-day embryo.

5. Internal Ear
• In embryos 22 days a thickening of the surface
ectoderm on each side of the rhombencephalon, is the
first indication of the developing ear.
• These thickenings, the otic placodes, invaginate
rapidly and form the otic or auditory vesicles
(otocysts).
• Each vesicle divides into;
1. Ventral component that gives rise to the saccule and
cochlear duct .
2. Dorsal component that forms the utricle, semicircular
canals, and endolymphatic duct (Figs. 16.3– 16.6).
Together these epithelial structures form the
membranous labyrinth.

6. Transverse sections through the region of the rhombencephalon
showing formation of the otic vesicles. Note the statoacoustic ganglia.
24 days
27 days 4.5 weeks

7. C to E. Cochlear duct at 6, 7, and 8 weeks,
respectively. Note formation of the ductus
reuniens and the utriculosaccular duct.
A and B. Development of
the otocyst showing a
dorsal utricular portion
with the endolymphatic
duct and a ventral saccular
portion.

8. SACCULE, COCHLEA, AND ORGAN OF CORTI
1/3
• In the sixth week of development, the saccule
forms a tubular outpocketing at its lower pole.
• This outgrowth, the cochlear duct, penetrates
the surrounding mesenchyme in a spiral
fashion until at the end of the eighth week it
has completed 2.5 turns.
• The ductus reuniens connects the remaining
portion of the saccule with utricle.

9. Development of the scala tympani and scala vestibuli. A. The cochlear duct is surrounded by a
cartilaginous shell. B. During the 10th week large vacuoles appear in the cartilaginous shell. C. The
cochlear duct (scala media) is separated from the scala tympani and the scala vestibuli by the basilar
and vestibular membranes, respectively. Note the auditory nerve fibers and the spiral (cochlear) ganglion.

10. • Mesenchyme surrounding the cochlear duct soon differentiates into
cartilage.
• In the 10th week, this cartilaginous shell undergoes vacuolization,
and two perilymphatic spaces, the scala vestibuli and scala
tympani.
• The vestibular membrane separates cochlear duct from the scala
vestibuli.
• The basilar membrane separates cochlear duct from the scala
tympani by.
• The spiral ligament attaches lateral wall of the cochlear duct to
the surrounding cartilage.
• The median angle of the cochlea angle is connected to and partly
supported by a long cartilaginous process, the modiolus, the future
axis of the bony cochlea.
SACCULE, COCHLEA, AND ORGAN OF CORTI
2/3

11. • The epithelial cells of the cochlear duct form two ridges:
1. The inner ridge, the future spiral limbus,
2. The outer ridge which forms the sensory cells, hair cells,
of the auditory system.
A. One inner row,
B. Three or four outer rows.
 They are covered by the tectorial membrane.
 The sensory cells and tectorial membrane together constitute
the organ of Corti.
 Impulses received by this organ are transmitted to the spiral
ganglion and then to the nervous system by the auditory
fibers of cranial nerve VIII.
SACCULE, COCHLEA, AND ORGAN OF CORTI
3/3

12. Development of the organ of Corti. A. 10 weeks. B. Approximately 5 months. C. Full-term
infant. Note the appearance of the spiral tunnels in the organ of Corti.

13. UTRICLE AND SEMICIRCULAR CANALS
1/2
• During the sixth week of development, semicircular canals appear
as flattened outpocketings of the utricular part of the otic vesicle.
Central portions of the walls of these outpocketings eventually
appose each other and disappear, giving rise to three semicircular
canals.
• Whereas one end of each canal dilates to form the crus ampullare,
the other, the crus nonampullare, does not widen.
• Five crura enter the utricle, three with an ampulla and two without.
• Cells in the ampullae form a crest, the crista ampullaris, containing
sensory cells for maintenance of equilibrium.
• Similar sensory areas, the maculae acusticae, develop in the walls
of the utricle and saccule.
• Impulses generated in sensory cells of the cristae and maculae as a
result of a change in position of the body are carried to the brain by
vestibular fibers of cranial nerve VIII.

14. 16.6 Development of the semicircular canals. A. 5 weeks. C. 6 weeks. E. 8 weeks.
B, D, and F. Apposition, fusion, and disappearance, respectively, of the central portions
of the walls of the semicircular outpocketings. Note the ampullae in the semicircular
canals.

15. 16.7 A. Transverse section of a 7-
week embryo in the region of the
rhombencephalon, showing the
tubotympanic recess, the first
pharyngeal cleft, and mesenchymal
condensation, foreshadowing
development of the ossicles.
B. Middle ear showing the cartilaginous
precursors of the auditory ossicles. Thin
yellow line in mesenchyme indicates
future expansion of the primitive
tympanic cavity. Note the meatal plug
extending from the primitive auditory
meatus to the tympanic cavity.

16. Ear showing the external auditory meatus, the middle
ear with its ossicles, and the inner ear.

17. • The statoacoustic ganglion forms during
formation of the otic vesicle, .
• The ganglion splits into cochlear and vestibular
portions,
• Supply sensory cells of the organ of Corti and
those of the saccule, utricle, and semicircular
canals, respectively.
UTRICLE AND SEMICIRCULAR CANALS
Statoacoustic ganglion
2/2

18. Middle Ear
TYMPANIC CAVITY AND AUDITORY TUBE
• The tympanic cavity is derived from the first
pharyngeal pouch.
• This pouch expands in a lateral direction and
comes in contact with the floor of the first
pharyngeal cleft.
• The distal part of the pouch gives rise to the
tubotympanic recess.
• The proximal part gives rise to the auditory
tube (Eustachian tube).

19. B. Middle ear showing the handle of
the malleus in contact with the
eardrum. The stapes will establish
contact with the membrane in the oval
window. The wall of the tympanic
cavity is lined with endodermal
epithelium.
A. Derivatives of the first
three pharyngeal arches.
Note the malleus and
incus at the dorsal tip of
the first arch and the
stapes at that of the
second arch.

20. OSSICLES 1/2
• The malleus and incus are derived from cartilage of the first pharyngeal
arch,
• The stapes is derived from that of the second arch.
• The ossicles appear during the first half of fetal life,
• they remain embedded in mesenchyme until the eighth month.
• When the ossicles are entirely free of surrounding mesenchyme, the
endodermal epithelium connects them in a mesentery-like fashion to the
wall of the cavity.
• The supporting ligaments of the ossicles develop later within these
mesenteries
• Since the malleus is derived from the first pharyngeal arch, its muscle, the
tensor tympani, is innervated by the mandibular branch of the trigeminal
nerve.
• The stapedius muscle, which is attached to the stapes, is innervated by
the facial nerve, the nerve to the second pharyngeal arch. ts of the
ossicles develop later within these mesenteries.

21. • During late fetal life, the tympanic cavity expands
dorsally by vacuolization of surrounding tissue to form
the tympanic antrum.
• After birth, epithelium of the tympanic cavity invades
bone of the developing mastoid process, and
epithelium-lined air sacs are formed (pneumatization).
• Later, most of the mastoid air sacs come in contact
with the antrum and tympanic cavity.
• Expansion of inflammations of the middle ear into the
antrum and mastoid air cells is a common complication
of middle ear infections.
OSSICLES 2/2

22. • EXTERNAL AUDITORY MEATUS.
• EARDRUM OR TYMPANIC MEMBRANE.
• AURICLE.
External Ear

23. External Ear
EXTERNAL AUDITORY MEATUS
• The external auditory meatus develops from the
dorsal portion of the first pharyngeal cleft.
• At the beginning of the third month, epithelial
cells at the bottom of the meatus
proliferate, forming a solid epithelial plate, the
meatal plug.
• In the seventh month, this plug dissolves and the
epithelial lining of the floor of the meatus
participates in formation of the definitive
eardrum.
• Occasionally the meatal plug persists until
birth, resulting in congenital deafness.

24. B. Middle ear showing the handle of
the malleus in contact with the
eardrum. The stapes will establish
contact with the membrane in the oval
window. The wall of the tympanic
cavity is lined with endodermal
epithelium.
A. Derivatives of the first
three pharyngeal arches.
Note the malleus and
incus at the dorsal tip of
the first arch and the
stapes at that of the
second arch.

25. EARDRUM OR TYMPANIC MEMBRANE
• The eardrum is made up of;
1. Ectodermal epithelial lining at the bottom of the
auditory meatus,
2. Endodermal epithelial lining of the tympanic cavity.
3. Intermediate layer of connective tissue that forms
the fibrous stratum.
 The major part of the eardrum is firmly attached to
the handle of the malleus,
 and the remaining portion forms the separation
between the external auditory meatus and the
tympanic cavity

26. AURICLE
• The auricle develops from six mesenchymal proliferations
at the dorsal ends of the first and second pharyngeal
arches, surrounding the first pharyngeal cleft.
• These swellings (auricular hillocks), three on each side of
the external meatus, later fuse and form the definitive
auricle.
• As fusion of the auricular hillocks is
complicated, developmental abnormalities of the
auricle are common.
• Initially, the external ears are in the lower neck region, but
with development of the mandible, they ascend to the side
of the head at the level of the eyes.

27. B to D. Fusion and
progressive development
of the hillocks into the
adult auricle
A. Lateral view of the head of
an embryo showing the six
auricular hillocks surrounding
the dorsal end of the first
pharyngeal cleft

28. G. External ear nearly
complete. Growth of the
mandible and neck region
places the ears in their
permanent position.
E. The six auricular
hillocks from
the first and second
pharyngeal arches.
H, heart; NP, nasal
placode
F.The hillocks becoming
more defined. Note the
position of the ears with
respect to the mouth and
eyes (e).

29. C L I N I C A L C O R R E L A T E S
Deafness and External Ear Abnormalities
• Congenital deafness, usually associated with deaf-mutism, may be
caused
– Abnormal development of the membranous and bony labyrinths,
– Malformations of the auditory ossicles and eardrum.
– In the most extreme cases the tympanic cavity and external meatus are
absent.
 Most forms of congenital deafness are caused by genetic factors,
 but environmental factors may also interfere with normal development of
the internal and middle ear;
1. Rubella virus, affecting the embryo in the seventh or eighth week, may
cause severe damage to the organ of Corti.
2. It has also been suggested that poliomyelitis,
3. Erythroblastosis fetalis,
4. Ddiabetes,
5. Hypothyroidism,
6. Toxoplasmosis can cause congenital deafness.

30. • External ear defects are common; they include minor
and severe abnormalities
They are significant from the standpoint of the
psychological and emotional trauma they may cause
and for the fact they are often associated with other
malformations.
 Thus, they serve as clues to examine infants carefully
for other abnormalities.
 All of the frequently occurring chromosomal
syndromes and most of the less common ones have
ear anomalies as one of their characteristics.
External Ear Defects 1/2

31. 16.11 A. Microtia with preauricular pit
(arrow). B. Preauricular pits (arrows).
C and D. Preauricular appendages (skin tags).
Note the low position of the tag in D.

32. • Preauricular appendages and pits are skin
tags and shallow depressions, respectively,
anterior to the ear.
• Pits may indicate abnormal development of
the auricular hillocks,
• whereas appendages may be due to
accessory hillocks.
• Like other external ear defects, both are
associated with other malformations.
External Ear Defects 2/2