Ethmoid sinus
The ethmoid sinuses or ethmoid air cells of the ethmoid bone are one of the four paired paranasal sinuses. The cells are variable in both size and number in the lateral mass of each of the ethmoid bones and cannot be palpated during an extraoral examination. They are divided into anterior and posterior groups. The ethmoid air cells are 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 lamellae. Groups of sinuses. The groups of the ethmoidal air cells drain into the nasal meatuses. The two groups are divided by the basal lamella. This is one of the bony divisions of the ethmoid bone and is mostly contained inside the ethmoid labyrinth. Medially the lamella becomes the bony part of the middle concha. Development. The ethmoidal cells (sinuses) and maxillary sinuses are present at birth. Innervation. The ethmoidal air cells receive sensory fibers from the anterior and posterior ethmoidal nerves, and the orbital branches of the pterygopalatine ganglion, which carry the postganglionic parasympathetic nerve  fibers for mucous secretion from the facial nerve. Haller cell. Haller cells are infraorbital ethmoidal air cells lateral to the lamina papyracea. These may arise from the anterior or posterior ethmoidal sinuses. Pathology. Acute ethmoiditis in childhood and ethmoidal carcinoma may spread superiorly causing meningitis and cerebrospinal fluid leakage or it may spread laterally into the orbit causing proptosis and diplopia.