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ethmoidal air cells; evaginations of the mucous membrane of the middle and superior meatus of the nasal cavity into the ethmoidal labyrinth forming multiple small paranasal sinuses; they are subdivided into anterior, middle and posterior ethmoidal sinuses. See: anterior ethmoidal cells, middle ethmoidal cells, posterior ethmoidal cells.
paranasal sinuses occurring in groups within the ethmoid bone and communicating with the ethmoidal infundibulum and bulla and the superior and highest meatus. They are often subdivided into anterior, middle, and posterior ethmoid cells, groups of air cells named according to where they open into the nasal meatus. Also called ethmoid sinuses. Compare frontal sinus, maxillary sinus, sphenoidal sinus.
eth·moid cells(ethmoyd selz)
Evaginations of the mucous membrane of the middle and superior meatus of the nasal cavity into the ethmoidal labyrinth forming multiple small paranasal sinuses.