Respuesta :

a cavity within a bone or other tissue, especially one in the bones of the face or skull connecting with the nasal cavities.
LittleStudent

Answer:

An air-filled cavity in a dense portion of a skull bone. The sinuses decrease the weight of the skull. The sinuses are formed in four right-left pairs. The frontal sinuses are positioned behind the forehead, while the maxillary sinuses are behind the cheeks.