what are the sinuses and what do they do?

The sinuses are hollow boxes in the skeleton of the face
which are filled with air. They are lined with a mucus
producing membrane.

The cilia on the sinus lining beat and carry mucus through small drainage holes, from the sinuses into narrow nooks, crannies and gutters in the sidewalls of the nose. These holes also allow air into the sinuses to keep them healthy.

If the face or head is injured the sinuses may absorb some of the impact and protect the brain and eyes like the 'crumple zones' of a car.

The sinuses also act as resonating chambers for the voice.