Ethmoid Sinus

Ethmoid Sinus

The ethmoid sinuses of the ethmoid bone are two of the four paired paranasal sinuses. They are composed of a variable number of air cells and divided into the anterior, middle and posterior groups. The ethmoidal air cells consist of numerous thin-walled cavities situated in the ethmoidal labyrinth and completed by the frontal, maxilla, lacrimal, sphenoidal, and palatine bones. They lie between the upper parts of the nasal cavities and the orbits, and are separated from these cavities by thin bony laminae.