Ethmoid bone

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.

  • * Song W, et al. Role of medial orbital wall morphologic properties in orbital blow-out fractures. Invest Ophthalmol Vis Sci. 2009;50(2):495-499.
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    Ethmoid bone ex situ Ethmoid bone in situ
    Ethmoid bone ex situ & in situ.
    Ethmoid bone ex situ & in situ. 360° rotation.
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    Front view of ethmoid bone
    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
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    Upper iso view of ethmoid bone
    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
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    Top view of ethmoid bone
    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
  • * Abdullah B, et al. Anatomical variations of anterior ethmoidal artery and their significance in endoscopic sinus surgery: a systematic review. Surg Radiol Anat, 2019;41(5):491-499.
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    Inferior iso view of ethmoid bone
    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
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    Lateral view of ethmoid bone
    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
  • 1 Landsberg R, Friedman M. A computer-assisted anatomical study of the nasofrontal region. Laryngoscope, 2001;111(12):2125–30.
  • 2 Nayak D, Balakrishnan R, et al. Functional anatomy of the uncinate process and its role in endoscopic sinus surgery. Indian J Otolaryngol Head Neck Surg, 2001;53(1):27–31.
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    The skeletotopy of ethmoid cells. 360° rotation.
    First published: 16/Apr/2019
    Last update: 07/Nov/2020