The mucosa that lines the nasal cavity extends into its chambers, the paranasal sinuses.
The nasal cavity and the paranasal sinuses are referred to as the sinonasal tract or sinonasal region, and its anatomy is recognised as being unique and complex.
Four paired paranasal sinuses – the frontal sinus, the sphenoid sinus, the ethmoid sinus and the maxillary sinus drain into regions of the nasal cavity.

The sinuses are air-filled extensions of the nasal cavity into the cranial bones.
The frontal sinuses are located in the frontal bone; the sphenoidal sinuses in the sphenoid bone; the maxillary sinuses in the maxilla; and the ethmoidal sinuses in the ethmoid bone.

A narrow opening called a sinus ostium from each of the paranasal sinuses allows drainage into the nasal cavity.
The maxillary sinus is the largest of the sinuses and drains into the middle meatus.
Most of the ostia open into the middle meatus and the anterior ethmoid, that together are termed the ostiomeatal complex.
Adults have a high concentration of cilia in the ostia.
The cilia in the sinuses beat towards the openings into the nasal cavity.
The increased numbers of cilia and the narrowness of the sinus openings allow for an increased time for moisturising, and warming.
The mucosa that lines the nasal cavity extends into its chambers, the paranasal sinuses. The nasal cavity and the paranasal sinuses are referred to as the sinonasal tract or sinonasal region, and its anatomy is recognised as being unique and complex. Four paired paranasal sinuses – the frontal sinus, the sphenoid sinus, the ethmoid sinus and the maxillary sinus drain into regions of the nasal cavity.
The sinuses are air-filled extensions of the nasal cavity into the cranial bones. The frontal sinuses are located in the frontal bone; the sphenoidal sinuses in the sphenoid bone; the maxillary sinuses in the maxilla; and the ethmoidal sinuses in the ethmoid bone.
A narrow opening called a sinus ostium from each of the paranasal sinuses allows drainage into the nasal cavity. The maxillary sinus is the largest of the sinuses and drains into the middle meatus. Most of the ostia open into the middle meatus and the anterior ethmoid, that together are termed the ostiomeatal complex. Adults have a high concentration of cilia in the ostia. The cilia in the sinuses beat towards the openings into the nasal cavity. The increased numbers of cilia and the narrowness of the sinus openings allow for an increased time for moisturising, and warming.
Human nose