Inferior endoscopic view of ethmoid bone and ethmoidal foramina. 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. Along or near the frontoethmoidal suture on the medial wall of the orbits are the anterior and posterior ethmoidal foramina that lead to canals that transmit neurovasculature bundles of corresponding names into the ethmoid labyrinth and nasal cavity. The arteries are branches of the ophthalmic artery; the nerves, branches of the nasociliary nerve. The veins are tributary to the superior ophthalmic vein. Anterior and lateral to the cribriform plate is the frontal sinus and posterior to the posterior-most ethmoid air cell is the sphenoid sinus. (Image courtesy of AL Rhoton, Jr.)