An ethmoid bone is a very particular bone localized between eyeballs and making a significant part of the nasal cavity. By the way, it is the most fragile bone in our body — made almost entirely by thin bony lamellae. Usually, ethmoid isn't present in skulls available for learning in Anatomy departments. The reason behind it is that some students grab the skull by putting fingers in orbits and applying some pressure over ethmoid bone. One action like this is enough to impress 0.2–0.4 mm* thin lamina papyracea into the labyrinthus ethmoidalis and destroy it.
Ethmoid bone ex situ & in situ.Ethmoid bone ex situ & in situ. 360° rotation.
The anterior aspect of ethmoid demonstrates this bone's main parts: midline lamina perpendicularis extending upward as crista galli and lateral parts of this bone containing conchas and ethmoid cells, collectively called labyrinthus ethmoidalis.
The list of terms:Crista galli Labyrinthus ethmoidalis – Ethmoidal labyrinth Lamina perpendicularis – Perpendicuar plate
Frontal iso view of ethmoid bone showing the same structures as the image above, plus the lamina cribrosa — the horizontally oriented bony plate that attaches lamina perpendicularis to the labyrinthus ethmoidalis. The lamina cribrosa is with multiple openings — cribrae — that connect intracranial space with the nasal cavity.
The list of terms:Crista galli Lamina cribrosa – Cribriform plate Lamina perpendicularis – Perpendicular plate Labyrinthus ethmoidalis – Ethmoidal labyrinth
Top view of the ethmoid bone. Note multiple ethmoid cells that open on top of an ethmoid labyrinth. The most ventral ethmoid cells communicate with the frontal sinus, and the dorsal ones are covered by the pars orbitalis ossis frontalis. Foramen ethmoidale anterius localized on orbit's medial wall connects orbit with the fossa cranii anterior via channel bordered by ethmoid bone (channel's floor) and the frontal bone (the channel's roof). This channel is known as canalis ethmoidalis anterior, is about 6 mm long, and contains clinically important a. ethmoidalis anterior*.
The list of terms:Lamina perpendicularis – Perpendicular plate Crista galli Ala cristae galli – Wings of crista galli Cellulae ethmoidales – Ethmoidal air cells Lamina cribrosa – Cribriform plate Foramina cribrosa – Cribriform foramina Foramen ethmoidale anterius – Anterior ethmoidal foramen Foramen etnmoidale posterius – Posterior ethmoidal foramen
Inferior ventral view of ethmoid bone demonstrating multiple exposed cellulae ethmoidales anteriores that in situ are covered by the frontal bone with frontal sinus from the top and with lacrimal bone from aside.
The list of terms:Cellulae ethmoidales anteriores — Anterior ethmoid cells Cellulae ethmoidales mediae — Middle ethmoid cells Cellulae ethmoidales posteriores — Posterior ethmoid cells Bulla ethmoidalis — Bulla of ethmoid
Lateral view of ethmoid bone. Note the processus uncinatus — the tiny plate of a complex shape bending along to the bulla ethmoidalis and, in most cases, anteriorly attached to the lamina papyracea1. Processus uncinatus is believed to play an essential role in the prevention of the non-sterile inspired air from contacting the sinus surface and directing the sterile expired air toward the sinuses2.
The list of terms:Crista galli Ala cristae galli – Wings of crista galli Lamina orbitalis (papyracea) – Orbital plate (paper-thin) Lamina perpendicularis – Perpendicular plate Bulla ethmoidalis Processus uncinatus – Uncinate process Infundibulum – Ethmoidal infundibulum Concha nasalis media – Middle nasal concha Concha nasalis superior – Superior nasal concha