Facial sinuses. X-ray of the skull of a 16-year- old girl, showing the facial sinuses. The sinuses, cavities in bones, appears as dark areas. The two frontal sinuses (in the frontal bone of the fore- head) are just above and between the eye sockets. Below the frontal sinuses are the two ethmoidal sinuses (in the bones between the nasal cavity and the eye sockets). The two large, dark areas in the cheeks are the maxillary sinuses (in the cheek- bones). The sinuses lighten the skull, make the voice more resonant, and produce mucus that drains into the nose. Infection, often provoked by a cold, causes sinusitis, where the mucous membrane lining the sinuses becomes inflamed.