It describes the embryology and anatomy of the human external ear according to the various books used for reference

2. Auricle – First branchial cleft is the precursor of
external auditory canal. At around 6th week of IUL, six
tubercles appear around 1st branchial cleft. They fuse to
form the auricle.
Tragus – develops from the tubercle of the first arch while
the rest of the pinna develops from the remaining 5
tubercles of the second arch
Faulty fusion between the first and second arch tubercles
causes preauricular sinus or cyst.

3. External auditory meatus – it develops from the
first branchial cleft by 16th embryonic week. Cells
proliferate from the bottom of ectodermal cleft and
form a meatal plug.
Recanalization of this plug forms the epithelial
lining of the bony meatus , it begins from the
deeper part near the Tympanic membrane and
progresses outwards

4. Tympanic membrane – it develops from all the
three germinal layers Outer epithelial layer is
formed by ectoderm, Inner mucosal layer by
endoderm and middle fibrous layer by mesoderm.
 Middle ear cleft – First and partly second
pharyngeal pouch form the tubo tympanic recess
the endoderm of tubo tympanic recess forms the
eustachian tube, tympanic cavity, attic, antrum
and mastoid air cells.
Malleus and incus are derived from mesoderm of
the first arch .

5. Stapes develops from the second arch except its
footplate and annular ligament which are derived
from the otic capsule.

6. Membranous inner ear – development of the
inner ear starts at 3rd week and completes by
16th week of IUL.
The ectoderm region of hindbrain thickens to
form an AUDITORY PLACODE, which is
invaginated to form auditory vesicle or
OTOCYST.
Otocyst- differentiates into endolymphatic
duct and sac ; the utricle, the semicircular
ducts ; and saccule and cochlea.

7. Pars superior (semicircular canals and utricle) takes
place earlier than pars inferior (saccule and
cochlea).

8. Organ of corti- it starts developing as a single
block of heaped up ectodermal cells at about 11
weeks within this mass develop inner , outer hair
cells & specialized supporting cells.
The tunnel of corti appears between inner and
outer pillar cells as clusters of stereocilia and
single kinocilium are developing on each hair cell.
The cochlear kinocilium regresses
The dark cell region- epithelium close to sensory
region develop into specialised cell groups which
maintain ionic and electrical stability of the
endolymph.

9. The bony labyrinth – mesenchyme enclosing the
otocyst becomes chondritified to form the otic capsule. The
membranous labyrinth expands, the otic capsule remodels
and in places undergoes dedifferentiation to form fluid
filled spaces called perilymphatic spaces.
The perilymphatic space become continuous and a
communication with csf is formed by development of
cochlear aqueduct, which runs to the post. Cranial fossa.
Most important channel that remains within otic capsule
is oval window, where part of otic capsule becomes stapes
footplate and annular ligament.

10. The temporal bone – is formed by 1)
petromastoid complex 2)squamous portion
3)tympanic bone 4) styloid process.
Petromastoid complex- derived from petrous bone,
it forms the roof of middle ear, layeral wall of
eustachian tube, floor of middle ear, canal of facial
nerve & petrous apex.
The squamous bone – it develops from
mesenchyme, it forms the lateral wall of foetal
mastoid antrum.

11. The tympanic bone develops from mesenchyme, but
from several centres around the external Meatus.
These form the major part of a ring with a groove on
the inner aspect that becomes the sulcus for TM.
The styloid develops from 2 centres at the cranial
end of the second arch. (reicherts) cartilage.
The petrous bone undergoes generalized downward
rotation, this makes the neonatal Horizontal TM to
an angle of 55 ° in adults.

12. The external ear consists of 1)auricle or pinna, 2)external
acoustic canal & 3)tympanic membrane.
Auricle /Pinna – The entire pinna except its lobule and
outer part of external auditory canal are made up of a
single piece of yellow elastic cartilage covered with skin.

13. There is no cartilage between the tragus and crus of
helix, and this area is called incisura terminalis. An
incision in this area will not cut through cartilage used in
endaural approach in surgery of EAC or mastoid.
External auditory canal – it extends from the bottom of
concha to the tympanic membrane and measures about
24mm along its posterior wall.
It is not a straight tube, its outer part is directed upwards,
backwards and medially while its inner part is directed
downwards, forwards and medially
The canal is divided into two parts 1)cartilaginous &
2)bony.

14. Cartilaginous part – it forms outer 1/3 of the
canal 8mm. Cartilage is continuation of the
cartilage which forms the framework of the
pinna.
It has 2 deficiencies – 1) fissures of Santorini
through them the parotid or superficial mastoid
infection appear in the canal or vice versa.
The skin covering the cartilaginous canal is thick
and contains ceruminous and pilosebaceous glands
which secrete wax, hair is only confined to outer
canal and hence furuncles are only seen in outer
1/3 of the canal

15. Bony part – it forms inner 2/3 (16mm).Skin
lining the bony canal is thin and continuous
over the tympanic membrane. It is devoid of
hair and ceruminous glands.
About 6 mm lateral to tympanic membrane,
the bony meatus presents a narrowing called
isthmus, foreign bodies, lodged medial to the
isthmus, get impacted.
Anterior recess –it is present in anteroinferior
part of the deep meatus, beyond the isthmus,
it acts like a cesspool for discharge and debris
in cases of external and middle ear infections.

16. Foramen of huschke – it is deficiency present in
the anteroinferior part of the bony canal.
Tympanic membrane – it forms the partition
between external acoustic canal and middle ear.
It is obliquely set and as a result, its
posterosuperior part is more lateral than its
anteroinferior part.
Tympanic membrane can be divided into 2 parts –
1)pars tensa 2)pars flaccida

17. Pars Tensa – forms most of the tympanic
membrane, its periphery is thickened to form
a fibro cartilaginous ring called annulus
tympanicus, which fits the tympanic sulcus.
The central part of pars tensa is tented
inwards at the level of tip of malleus and is
called umbo
A bright cone of light can be seen radiating
in the anteroinferior quadrant.

18. Pars flaccida (Shrapnell’s Membrane) – This is
situated above the lateral process of malleus
between notch of Rivinus and the anterior and
posterior malleal folds (earlier called malleolar
folds)
Layers of tympanic membrane – 1)Outer
epithelial layer 2)Inner mucosal layer 3)Middle
fibrous layer – encloses handle of malleus and
has 3 fibres – the radial, circular and parabolic.
Outer epithelial layer is continuous with the skin
lining of meatus, inner mucosal layer is continous
with mucosa of middle ear

20. Relations of the external
acoustic meatus
1) Superiorly – Middle
cranial fossa
2) Posteriorly – Mastoid air
cells and the facial nerve
3) Inferiorly – Parotid gland
4) Anteriorly –
Temporomandibular joint.

21. Nerve supply of the external ear.
Pinna – 1)Greater auricular nerve (C2, 3)
supplies most of the medial surface of pinna and
only posterior part of lateral surface.
2)Lesser occipital (C2) supplies upper
part of the medial surface.
3)Auriculotemporal (V3) supplies the
tragus, crus of helix and the adjacent part of the
helix.
4) Auricular branch of vagus (CN X), also
called Arnold’s nerve, supplies the concha and
corresponding eminence of medial surface.
5) Facial nerve – supplies the concha and
retroauricular groove.

22. External auditory canal – 1)Anterior wall and roof is
supplied by Auriculotemporal (V3)
2) Posterior wall and floor : Auricular branch of vagus
(CN X)
3) Posterior wall of the auditory canal also receives
sensory fibres of CN VII through auricular branch of
vagus.
Tympanic membrane – 1)Anterior half of lateral
surface :Auriculotemporal (V3)
2) Posterior half of the lateral surface :Auricular branch
of vagus (CN X)
3) Medial surface :tympanic branch of CN IX
(Jacobson’s nerve)