nasal fossa, one of the pair of approximately equal chambers of the nasal cavity that are separated by the nasal septum and open externally through the nares and internally into the nasopharynx through the internal nares. Each fossa is divided into an olfactory region, consisting of the superior nasal concha and part of the septum, and a respiratory region, constituting the rest of the chamber. Overhanging the three meatuses of each fossa on the lateral wall are the corresponding superior, middle, and inferior nasal conchae. The superior meatus extends obliquely about halfway along the superior border of the middle concha. The middle meatus continues into the atrium and bulges on the lateral wall at the bulla ethmoidalis. The inferior meatus courses below and laterally to the inferior nasal concha and contains the opening of the nasolacrimal duct. The olfactory region is located in the most superior part of the fossa and contains olfactory cells, olfactory nerves, and olfactory hairs. The respiratory region is lined with mucous membrane, numerous glands, nerves, a plexus of dilated veins, and blood spaces. The plexus is easily irritated, causing the membrane to swell, blocking the meatuses and the openings of sinuses.
