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Ethmoid bone

Anatomy, function and location of the ethmoid bone.

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Hello once again! It’s Matt from Kenhub, and in this tutorial, we will be talking about the ethmoid bone. The ethmoid bone is a singular porous bone that makes up the middle area of the viscerocranium and forms the mid-facial region of the skull. It is an unpaired bone in the ethmoid notch of the frontal bone that contributes to the molding of the orbit, nasal cavity, nasal septum and the floor of the anterior cranial fossa.

The bone consists of a perpendicular plate which you can see highlighted in green on this image and two ethmoidal labyrinths which are all superiorly attached to the cribriform plate. This green highlight shows the orbital part of the ethmoid which extends towards the orbit. This part forms the medial wall of the orbit. The ethmoid labyrinths lie on both lateral sides and contain numerous little cavities with ethmoidal cells which are referred to as the ethmoidal sinus. These ethmoidal air cells are situated between the orbital and nasal cavities. The labyrinths formed two of the biggest structures in the nasal cavity – the superior and middle nasal conchae – which arise from the perpendicular plate of the ethmoid bone.

The hiatus semilunaris separates the ethmoid bulla and the uncinate process. It constitutes the connection between the frontal and maxillary sinuses to the anterior ethmoidal cells. It also provides an opening for the infundibulum. The perpendicular plate of the ethmoid bone is a thin lamina which runs horizontally from the cribriform plate. Inferiorly, it attaches to the septal cartilage of the nose thus forming the upper part of the nasal septum. The cribriform plate lies within the ethmoidal notch of the frontal bone and forms the roof of the nasal cavity. In Latin, cribriform means "perforated". As the name suggests, it comprises numerous openings through which the olfactory nerve fibers from the nasal cavity pass through to the anterior cranial fossa.

The falx cerebri is attached to the crista galli which is this small vertical protrusion on top of the plate seen here highlighted in green. The olfactory bulbs lies on two grooves lateral to the crista galli. Because of its central location within the skull, the ethmoid bone comes in contact with 15 other bones of the skull. The most important borders are anteriorly to the frontal bone, posteriorly with the sphenoid bone, and inferiorly to the vomer and inferior nasal concha.

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