On the lateral wall of the nasal cavity are the superior, middle, and inferior nasal conchæ, and below and lateral to each concha is the corresponding nasal passage or meatus. Above the superior concha is a narrow recess, the sphenoethmoidal recess, into which the sphenoidal sinus opens. The superior meatus is a short oblique passage extending about half-way along the upper border of the middle concha; the posterior ethmoidal cells open into the front part of this meatus. The middle meatus is below and lateral to the middle concha, and is continued anteriorly into a shallow depression, situated above the vestibule and named the atrium of the middle meatus. On raising or removing the middle concha the lateral wall of this meatus is fully displayed. On it is a rounded elevation, the bulla ethmoidalis, and below and in front of this is a curved cleft, the hiatus semilunaris.