Middle meatus

The middle meatus is situated between the middle and inferior conchæ, and extends from the anterior to the posterior end of the latter.

The lateral wall of this meatus can be satisfactorily studied only after the removal of the middle concha.

On it is a curved fissure, the hiatus semilunaris, limited below by the edge of the uncinate process of the ethmoid and above by an elevation named the bulla ethmoidalis; the middle ethmoidal cells are contained within this bulla and open on or near to it.

Through the hiatus semilunaris the meatus communicates with a curved passage termed the infundibulum, which communicates in front with the anterior ethmoidal cells and in rather more than fifty per cent. of skulls is continued upward as the frontonasal duct into the frontal air-sinus; when this continuity fails, the frontonasal duct opens directly into the anterior part of the meatus.

Below the bulla ethmoidalis and hidden by the uncinate process of the ethmoid is the opening of the maxillary sinus (ostium maxillare); an accessory opening is frequently present above the posterior part of the inferior nasal concha.