Sinus cavity

The paranasal sinuses are eight (four pairs) air-filled spaces, or sinuses, within the bones of the skull and face. These are divided into subgroups that are named according to which bones they lie under;

• the maxilliary sinuses, also called the antra, are under the eyes, in the upper jawbone.
• the frontal sinuses, over the eyes, in the bone of the forehead.
• the ethmoid sinuses, between the nose and the eyes, backwards into the skull.
• the nasal cavity via small orifices called ostia. These become blocked relatively easily by allergic inflammation, or by swelling in the nasal lining which occurs with a cold. If this happens, normal drainage of mucus within the sinuses is disrupted, and sinusitis may occur.