Definition for Paranasal sinus
From Biology Forums Dictionary
1. Are a group of four paired air-filled spaces that surround the nasal cavity (maxillary sinuses), above the eyes (frontal sinuses), between the eyes (ethmoid sinuses), and behind the ethmoids (sphenoid sinuses). The sinuses are named for the facial bones in which they are located.
2. Are mucous membrane-lined cavities in the frontal, maxillary, sphenoid and ethmoid bones.