Anatomy of Your Sinus Cavities

The sinuses are air-filled bony cavities located in the face and skull adjacent to the nose. There are four pairs of sinuses. The right and left frontal sinuses are found in the forehead region, the maxillary sinuses are in the cheek area, the ethmoid sinuses are between the eyes, and the sphenoid sinuses lie deep in the center of the skull. Each sinus is connected to the nose by a small opening called an ostium. All except the frontal sinuses begin growing before birth as small pockets approximately the size of a pea. They increase in size through childhood until they are about as large as a walnut.

The purpose of the sinuses is not fully understood. Some experts maintain that they exist to lighten the skull, while others note that sinuses improve vocal resonance. Most physicians believe that their chief function is to produce a special mucus that keeps the inside of the nose moist and protects it from dust, dirt, pollutants, and microbiologic organisms. The mucus layer is propelled by tiny hair cells called cilia toward the back of the nose and throat, where it is swallowed.

Your head has a cavity, the nasal cavity, which connects directly to the nose, but is not part of the sinus. The important stuff, the cilia, are in the four sinuses, which each have left and right halves -
Frontal Sinuses - above your eyes, just behind the forehead.

Maxillary Sinus - to the side of the nose, and below the eye, just above the upper teeth, below the eyes and in back of the nose at the top of the throat.
Ethmoid Sinus - between the eyes (actually within the spongy ethmoid bone).
Sphenoid Sinus - WAY back in the head, far behind the eyes, above the throat (in back of the nasal cavity). This sinus is just forward of the brain case, making complications here quite serious.