Ethmoid bone from the right side.
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| colspan="2" |Coronal section of nasal cavities.
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|Latin
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|colspan="2"|[subject #36 ]
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|System
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|Precursor
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|MeSH
|colspan="2"|[A04.531.621.267]
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|Dorlands/Elsevier
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An ethmoid sinus is one of the four subtypes of paranasal sinuses. Each ethmoid sinus is an air-space enclosed within the ethmoid bone.
Anatomically, ethmoidal sinuses can be classified as the anterior, middle, and posterior ethmoid sinuses.
The anterior and middle ethmoidal sinuses drain into the middle meatus of the nose. The posterior ethmoidal sinuses drain into the superior meatus.
They lie between the upper parts of the nasal cavities and the orbits, and are separated from these cavities by thin bony laminæ.
On either side they are arranged in three groups, anterior, middle, and posterior.
The anterior and middle groups open into the middle meatus of the nose, the former by way of the infundibulum, the latter on or above the bulla ethmoidalis.
