Inferior endoscopic view of ethmoid bone complex. The cribriform plate of the ethmoid bone is the sieve-like structure in the center of this image. The perpendicular plate (largely removed except for a small ridge of bone) descends from its midline and forms part of the bony nasal septum. The ethmoidal labyrinth extends lateral from the margins of the cribriform plate and consists of medial or turbinal walls of nasal conchae (superior and middle) and orbital walls or plates that form much of the medial walls of the orbits. These vertical plates enclose a series of ethmoid air cells. Anterior and lateral to the cribriform plate is the frontal sinus. (Image courtesy of AL Rhoton, Jr.)