Features
The external auditory meatus conducts sound waves from the concha to the tympanic membrane.
The canal is S-shaped.
Its outer part is directed medially, forwards and upwards. The middle part is directed medially, backwards and upwards.
The inner part is directed medially, forwards and downwards.
The meatus can be straightened for examination by pulling the auricle upwards, backwards and slightly laterally.
The meatus or canal is about 24mm long,
of which the medial two-thirds or 16 mm is bony, and the lateral one-third or 8 mm is cartilaginous.
Due to the obliquity of the tympanic membrane, the anterior wall and floor are longer than the posterior wall and roof
The canal is oval in section.
The greatest diameter is vertical at the lateral end, and anteroposterior at the medial end.
The bony part is narrower than the cartilaginous part. The narrowest point, the isthmus, lies about 5 mm from the tympanic membrane.
The bony part is formed by the tympanic plate of the temporal bone which is C-shaped in cross-section.
The posterosuperior part of the plate is deficient.
Here the wall of the meatus is formed by a part of the squamous temporal bone.
The meatus is lined by thin skin, firmly adherent to the periosteum.
The cartilaginous part is also C-shaped in section;
the gap of the 'C' is filled with fibrous tissue. The lining skin is adherent to the perichondrium, contains hairs, sebaceous glands, and ceruminous or wax glands. Ceruminous glands are modified sweat glands.
Blood Supply
The outer part of the canal is supplied by the superficial temporal and posterior auricular arteries, and
the inner part, by the deep auricular branch of the maxillary artery.
Lymphatics
The lymphatics pass to preauricular, postauricular and superficial cervical lymph nodes.
Nerve Supply
The skin lining the anterior half of the meatus is supplied by the auriculotemporal nerve, the posterior half, by the auricular branch of the vagus.
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