Ethmoid bone (anterior and posterior views) (English)

The ethmoid is an unpaired bone situated in the midline of the skull. It consists of a centrally positioned crista galli, which is continued inferiorly by the perpendicular plate.On each side of the midline there is a spongy lateral mass, often referred to as the ethmoidal labyrinth. Each mass consists of numerous air-filled ethmoidal cells. Thus, each mass is known as the ethmoidal paranasal sinus. The lateral wall of the sinus presents a saccular extension called the ethmoid bulla, the largest of ethmoidal cells. Ethmoidal masses feature a hook-like projection pointing inferiorly called the uncinate process. This process forms a part of the wall of the maxillary sinus and is often confused as a part of the maxilla rather than of ethmoid. The lateral surface of ethmoidal masses faces the orbit, forming a part of its medial wall. The medial surface of each mass faces the perpendicular plate. From an anterior view, it is visible how a separate bony lamina called the middle nasal concha extends inferiorly from the root of each mass. The posterior view allows the appreciation of the superior nasal concha as well. The conchae project into the nasal cavity increasing its surface. Between the conchae is the middle nasal meatus, which drains the ethmoidal cells into the nasal cavity.