Ethmoid bone


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Ethmoid bone ex situ Ethmoid bone in situ
Ethmoid bone ex situ & in situ.
Ethmod is very particular bone localized between eyeballs and making the significant part of the nasal cavity. It is, by the way, the most fragile bone in our body — it's almost completely made 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 lamina papyracea into labyrinthus ethmoidalis and destroy it.

Ethmoid bone ex situ & in situ. 360° rotation.

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Front view of ethmoid bone Markup for front view of ethmoid bone
The anterior aspect of ethmoid demonstrating main parts of this bone: 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 Markup for 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 labyrinthus ethmoidalis. The lamina cribrosa is with multiple openings — cribrae — that connect intracranial space with 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 Markup for 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 (cellulae ethmoidales anteriores) directly opens into the frontal sinus, but dorsal ones are just covered by the pars orbitalis ossis frontalis . Foramen ethmoidale anterius localized on the medial wall of orbit connects with the fossa cranii anterior via channel bordered by ethmoid bone from above and the frontal bone from the top side. This channel in specialized literature is referred 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, Lim E et al. Anatomical variations of anterior ethmoidal artery and their significance in endoscopic sinus surgery: a systematic review. Surg Radiol Anat, 2018 [Epub ahead of print]

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    Inferior iso view of ethmoid bone Markup for the 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 Markup for the lateral view of ethmoid bone
    Lateral view of ethmoid bone. Note processus uncinatus — the tiny plate of a complex shape bending along to the bulla ethmoidalis and in the majority of cases, anteriorly attached to the lamina papyracea*. 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 sinuses**.
    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

  • * Landsberg R, Friedman M. A computer-assisted anatomical study of the nasofrontal region. Laryngoscope, 2001; 111(12):2125–30.
  • ** 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; 53:27–31.
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    The skeletotopy of ethmoid cells. 360° rotation.