The nasal cavity is a narrow space covered with mucus extending from the nostrils to the passageway to the pharynx (choana). It is divided into two halves (right and left) by a septum of cartridges. There are turbinates(lower, middle and upper) on both sides of the nasal cavity. There are also paranasal sinuses, bilateral air-filled spaces between the cranium and facial bones connected to the nasal cavity by the ostia. The sinuses have several important functions, such as humidifying air, making the voice resonate and providing protection.