In the course of RESPIRATION, incoming air enters via the nose and is here warmed, moistened, and filtered before entering the lungs. The nose has a protective function, irritant air being expelled by SNEEZING. It is also the organ of SMELL.

Several sinuses (see SINUS) lie concealed in the bones of the SKULL, into which air enters freely by apertures connecting them with the nose. These cavities occupy spaces in the frontal bone over the eyebrow (frontal sinus); in the upper jaw-bone, filling in the angle between the EYE and the nose (maxillary sinus); in the sphenoid bone (sphenoidal sinus); and in the lateral part of the ethmoid bone (ethmoidal sinus). The sinuses drain into the interior of the nose, as does the Eustachian or auditory tube from the middle ear (see EAR).