Ethmoid bone

The ethmoid bone is a singular porous bone that makes up the middle area of the viscerocranium and forms the midfacial region of the skull. It contributes to the moulding of the orbit, nasal cavity, nasal septum and the floor of the anterior cranial fossa.

Developing by the process of endochondral ossification, the ethmoid bone is an important piece of your skull, especially due to the cribriform plate, which allows the olfactory fibers to pass through in order for you to smell things.

This article will examine the important aspects and features of the ethmoid bone, together with its borders.

Key facts about the ethmoid bone
Ethmoidal labyrinths	Contain ethmoidal cells (little cavities) which form the ethmoidal sinus. The labyrinths form the superior and middle nasal conchae. The ethmoidal bulla is connected to the maxillary sinus via the hiatus semilunaris.
Perpendicular plate	It forms part of the nasal septum.
Cribriform plate	It forms the roof of the nasal cavity and has openings for the passage of olfactory fibers.
Borders	Anteriorly: frontal bone Posteriorly: sphenoid bone Inferiorly: vomer and inferior nasal concha
Osseous development	Endochondral ossification

Contents

Anatomy
Borders
Osseous development
Summary
Related diagrams and images

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Anatomy

Ethmoidal labyrinths

The bone consists of a perpendicular plate and two ethmoidal labyrinths parts which are all superiorly attached to the cribriform plate. A smaller orbital part extends towards 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. The labyrinths form two of the biggest structures in the nasal cavity: the superior and middle nasal concha. 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.

Structure and landmarks of the ethmoid bone

Perpendicular plate

The perpendicular plate is a thin lamina which runs vertically from the cribriform plate. Inferiorly it attaches to the septal cartilage of the nose and hereby forms part of the nasal septum.

Cribriform plate

The cribriform plate (Latin “cribriform” = perforated) lies within the ethmoidal notch of the frontal bone and forms the roof of the nasal cavity. As the name suggests it comprises numerous openings through which the olfactory fibers from the nasal cavity pass through to the anterior cranial fossa. The falx cerebri is attached to the crista galli (Latin “crista galli” = crest of the cock), a small vertical protrusion on top of the plate. The olfactory bulbs lie on two grooves lateral to the crista galli.

Borders

Because of its central location within the skull the ethmoid bone comes in contact with 15 other skull bones. The most important borders are:

anterior with the frontal bone
posterior with the sphenoid bone
inferior with the vomer and inferior nasal concha

Osseous development

The ethmoid bone ossifies completely by endochondral ossification. In newborns the labyrinths are relatively small and both the perpendicular and cribriform plates consists mainly out of cartilage. The latter start to ossify by the age of one and fuse with the labyrinths by the age of two to form a single ethmoid bone.

Summary

The ethmoid bone is a singular porous bone that makes up the middle area of the viscerocranium and forms the midfacial region of the skull. The bone consists of:

a perpendicular plate - a thin lamina which runs ventrally from the cribriform plate and forms part of the nasal septum.
two ethmoidal labyrinths - parts which are all superiorly attached to the cribriform plate. They contain numerous little cavities with ethmoidal cells which are referred to as the ethmoidal sinus
cribriform plate comprises numerous openings through which the olfactory fibers from the nasal cavity pass through to the anterior cranial fossa.

The ethmoid bone also has several borders, the most important being mentioned below:

Frontal lobe - anteriorly
Sphenoid bone - posteriorly
Vomer + Inferion nasal chonca - inferiorly

Related diagrams and images

Ethmoid bone

Anterior view of the skull

Midsagittal skull

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Ethmoid bone