Ethmoid bone

The ethmoid (Latin ethmoid bone ) is a bone of the skull. He is at the end of the nasal cavity on the border of the cranial cavity in depth and is therefore not under external view of the skull visible.

Exterior walls

The ethmoid consists of several plates of bone ( laminae ). In the median plane is the vertical Asked perpendicular lamina. This forms the posterior part of the nasal septum (septum nasi). The wafer-thin orbital plate (lamina orbital ) is the limit to the orbit and is called by people because of their tenderness and lamina papyracea.

In the other mammals, a distinction is beside the median perpendicular plate, roof plate (lamina tectoria ) as upper, orbital plate (lamina orbital ) as lateral and the bottom plate (lamina basalis ) as the lower outer wall.

The conclusion to the cranial cavity forms the sieve plate (lamina cribrosa ). This is a criss-crossed with many holes structure, from which the name for the bone. It stands in the primates almost horizontally on the roof of the nasal cavity in the other mammals, however, perpendicular at the end of the nasal cavity. Through the sieve plate pull the nerve fibers of the first cranial nerve ( olfactory nerve ) to the brain and the anterior ethmoidal nerve and the anterior ethmoidal artery ( from the ophthalmic artery ) to the nasal cavity. Cranial cavity side, the screen plate is recessed on both sides. In this wire pit ( fossa ethmoid ) straddle the olfactory bulb. Both Siebgruben are separated by the Hahnenkamm ( Crista galli ).

Internal structure

From the walls rise inside the so-called Siebbeinmuscheln ( Ethmoturbinalia ). It involves thin bony plates that roll up spirally. In their totality they form the ethmoidal labyrinth ( ethmoidal Labyrinthus ), the resulting deferred cavities is called the ethmoid cells ( ethmoid Cellulae ). In animals, the larger, widely known inwardly extending Ethmoturbinalia Endoturbinalia, the smaller Ectoturbinalia be. The Ethmoturbinalia form the bony basis of the upper and middle turbinates ( nasal concha superior ( in animals dorsalis) and media).

In humans and apes has the "simple" nose only three Turbinalia, of which the two upper spring of the ethmoid bone and the basis for the upper and middle turbinates ( nasal concha and superior media) form. The middle turbinate is of particular medical importance, since under their most sinuses, namely the maxillary sinus ( maxillary sinus ), the frontal sinus (sinus frontalis) and the anterior ethmoid cells ( ethmoid sinus anterior ) open into the nose. On the basis of the bony structures in this area, particularly the uncinate ( hooked extension ), the nasal mucosa, a funnel- shaped channel forms here ( ethmoidal infundibulum ) with crescent-shaped opening ( hiatus semilunaris ). Pathological changes in this area can be the cause of a chronic inflammation of the nasal sinuses. In this case, an attempt is made to achieve through operational opening of the infundibulum with removal of the hook extension ( infundibulotomy ) a normalization of ventilation of the sinuses.