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.anterior ethmoidal cells, middle ethmoidal cells, posterior ethmoidal cells SYN: cellulae ethmoidales [TA], ethmoid air cells [TA], ethmoidal cells [TA], antra ethmoidalia, ethmoidal sinuses, sinus ethmoidales.
