Anterior inferior view of the ethmoid bone. The ethmoid is a single, complex bone that occupies the central region of the viscerocranium. It has relationships with the orbit, nasal cavity, nasal septum, and anterior cranial fossa. It consists of two midline vertical projections, the crista galli and perpendicular plate, a pair of horizontal projections that form the roof of the nasal cavity, the cribriform plates, which connect to the ethmoid labyrinths. In this view, the crista galli projects superiorly and is one of sites of attachment of the falx cerebri. The perpendicular plate projects inferiorly to attach to the vomer and septal cartilage of the nasal septum. The cribriform plate is not visible in this orientation. The labyrinth consists of two laminae that enclose a series of ethmoid air cells. The lateral or orbital lamina is thin (lamina papyracea) and forms part of the medial wall of the orbit. The medial or turbinal lamina bears the superior and middle turbinates along the lateral wall of the nasal cavity. The uncinate process is a crescent-shaped projection from the posteroinferior aspect of the ethmoid labyrinth. The ethmoid bone attaches to the ethmoid notch of the frontal bone. (Image courtesy of PA Rubino)