The ear is divided into three parts - external, middle, and internal. The external ear consists of the pinna and external auditory meatus. The pinna has elevations like the helix and depressions like the concha. The middle ear contains the auditory ossicles and transmits sound from the tympanic membrane to the inner ear. The internal ear contains the membranous labyrinth within the bony labyrinth, and is responsible for hearing and balance. It includes the cochlea, saccule, utricle and semicircular canals.

1. BY DR. VIBHASH KUMAR VAIDYA

2. EAR
•The ear is the organ of hearing.
•It plays an important role in
maintaining the balance
(equilibrium) of the body.
•The ear is divided into three parts:
1. External ear.
2. Middle ear.
3. Internal ear.

3. EXTERNAL EAR
The external ear consists of:
(a) pinna or auricle and,
(b) external auditory meatus.
[which are concerned with collection and transmission of
sound waves to the tympanic membrane.]

4. AURICLE/PINNA
•The auricle is trumpet-like wave like pattern of
projection on the side of the head.
•The entire pinna except its lobule is made up of
a single piece of yellow elastic cartilage covered
with skin.
•The lobule of pinna is made of fibrofatty tissue
covered with skin.
•The auricular cartilage is continuous with the
cartilage of the external auditory meatus.

5. FEATURES
The auricle presents two surfaces: lateral and medial.
The lateral surface of auricle displays following
elevations and depressions:
1. Concha – A large depression that leads into the
external auditory meatus.
2. Helix- forms a prominent peripheral rim of the
pinna.
It consists of two limbs—anterior and posterior.
An anterior limb ends as crus of helix.
The posterior limb ends below as flabby ear lobe and its
upper end sometimes presents a small elevation called
Darwin’s tubercle.

6. 3. Antihelix- is another prominent ridge present in front
and parallel to the posterior part of helix, partly
encircling the concha.
Its upper end divides into two crura enclosing a triangular
depression called triangular fossa.
The narrow gutter between the helix and antihelix is
called scaphoid fossa.
4. Tragus- is a small triangular flap in front of concha.
5. Antitragus- is a small elevation opposite to tragus
from which it is separated by an intertragic notch.
6. Cymba conchae - is a small area of concha above the
crus of helix.
7. Lobule- of the ear hangs below the antitragus as a
large skin covered flap of fibrofatty tissue.

7. The medial/cranial surface of (pinna) presents the following features:
1. Eminentia concha- which corresponds to the depression of the concha.
2. Eminentia triangularis- which corresponds to the triangular fossa between the
crura of the antihelix.

8. EXTERNAL AUDITORY MEATUS
•The external auditory meatus (syn. external acoustic
meatus) extends from the bottom of the concha to the
tympanic membrane.
•Measures- about 24 mm along its posterior wall.
•It is not a straight tube but it has a typical S-shaped
course.
•Its outer part is directed upwards, backwards, and
medially (UBM), whereas its inner part is directed
downwards, forwards, and medially (DFM).
•Therefore, to examine the tympanic membrane the
pinna has to be pulled upwards, backwards, and
laterally, to bring the two parts in alignment. Parts
outer 1/3 (8 mm) inner two-third
(16 mm)

9. TYMPANIC MEMBRANE
•The tympanic membrane (or ear drum) is a thin
(0.1 mm thick) semitransparent membrane.
•It is forms the partition between external acoustic
meatus and middle ear.
•It is oval in shape.
•Measurements: 9–10 mm in length, and 8–9 mm
in width.
•It is placed obliquely making an angle of about 55°
with the floor of the external acoustic meatus.
•The tympanic membrane faces downwards,
forwards, and laterally as though to catch the
sounds reflected from the ground.

10. Structure:
The tympanic membrane is made of three layers.
Outer cuticular layer Middle fibrous layer Innermucosal layer

11. CLINICAL CORRELATION
The infection and boils of the external auditory meatus cause very little swelling
but are very painful because the skin lining is firmly adhered to the underlying
cartilage and bone.
Ear wax:- It prevents the injury of the lining epithelium of the external auditory
meatus from water and the damage of tympanic membrane by trapping the
insects.
The excess of ear wax interfering with hearing.
Perforation of the tympanic membrane:- It may result from an external injury
or middle ear infection (otitis media).

12. MIDDLE EAR
•The middle ear (syn. tympanum,
tympanic cavity) is a narrow slit-like
air-filled cavity within the petrous
part of the temporal bone.
•The middle ear is sandwiched
between the external and internal
ear.
•It contains three auditory ossicles,
which transmit sound vibrations from
tympanic membrane in its lateral wall
to the internal ear.

13. •From front to back, the diverticulum consists of pharyngotympanic tube,
tympanic cavity, and mastoid antrum.
•In a section through long axis of petromastoid bone, the outline of tympanic
cavity together with mastoid antrum and pharyngotympanic tube resembles a
pistol.

14. Size and Shape- The middle ear is shaped like a
cube, compressed from side to side.
In coronal section, it resembles a biconcave disc, like
a red blood cell.
Measurements-
1. Vertical diameter: 15 mm.
2. Anteroposterior diameter: 15 mm.
3. Transverse diameters:
(a) At roof: 6 mm.
(b) In the center: 2 mm.
(c) At the floor: 4 mm.

15. Communication The middle ear:
Anteriorly with nasopharynx through pharyngotympanic tube.
Posteriorly with mastoid antrum and mastoid air cells through aditus to antrum called aditus ad
antrum.
Contents of the Middle Ear:
Inside the mucous lining:
1. Air.
Outside the mucous lining:
1. Three small bones called ear ossicles: malleus, incus, and stapes.
2. Two muscles: tensor tympani and stapedius.
3. Two nerves: chorda tympani and tympanic plexus.
4. Vessels supplying and draining the middle ear.
5. Ligaments of the ear ossicles.

16. SUBDIVISIONS OF THE MIDDLE EAR
1. Epitympanum- a part above the tympanic
membrane containing head of malleus, body, and
short process of incus.
2. Mesotympanum- a part opposite to tympanic
membrane containing handle of malleus, long
process of incus, and stapes. It is the narrowest
part of the middle ear.
3. Hypotympanum- a part below the tympanic
membrane.

17. BOUNDARIES
The middle ear is likened to a six-
sided box and thus presents six
walls:
1. Roof.
2. Floor.
3. Anterior wall.
4. Posterior wall.
5. Medial wall.
6. Lateral wall.
O- oval window, P- pyramid, PC- processus cochleariformis, PM-
promontory, R- round window, S- sinus tympani, TP- tympanic plexus

18. CLINICAL CORRELATION
Infection of the middle ear (otitis media):- It is common especially in infants and children. Infective agents
reach the middle ear from the upper respiratory tract through pharyngotympanic tube.
The long-standing infection leads to chronic suppurative otitis media (CSOM).
Which clinically presents as ear discharge and perforation of tympanic membrane.
The spread of infection from the middle ear may give rise to the following clinical conditions:
– Acute mastoiditis and mastoid abscess, when infection spreads into mastoid antrum and mastoid air cells
through aditus ad antrum in the posterior wall.
– Meningitis and temporal lobe abscess may occur, if infection spreads upwards through the thin roof
(tegmen tympani).
– Lower motor neuron type of facial palsy, when infection erodes the papery thin bony wall of facial canal.
– Transverse and sigmoid sinus thrombosis, when infection spreads through the floor.

19. INTERNAL EAR
The internal ear consists of a closed system of fluid filled intercommunicating
membranous sacs and ducts called membranous labyrinth.
The fluid filled in the membranous labyrinth is called endolymph.
The membranous labyrinth lies within the complex intercommunicating bony cavities
and canals (bony labyrinth) in the petrous part of the temporal bone.
The space between the membranous and bony labyrinth is filled with fluid called
perilymph.
The sensory receptors within the membranous labyrinth are responsible for hearing
and balancing (equilibrium).

20. Components of the Internal Ear
The internal ear consists of two components:
1. Membranous labyrinth.
2. Bony labyrinth.

21. MEMBRANOUS LABYRINTH
The membranous labyrinth
consists of the following four parts:
1. Cochlear duct.
2. Saccule.
3. Utricle.
4. Semicircular ducts (three).
Complete
membranous
labyrinth.
Parts of
membranous
labyrinth.

22. BONY LABYRINTH
The bony labyrinth consists of a series
of intercommunicating bony cavities
and canals within the petrous part of
the temporal bone.
Parts-
The bony labyrinth presents three parts
from before backwards these are:
1. Cochlea.
2. Vestibule.
3. Semicircular canals (three).