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Ethmoid bone

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

The ethmoid bone is an important piece of the 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 anatomy, structure and function of the ethmoid bone.

Key facts about the ethmoid bone
Definition A small cuboidal bone that forms the lateral boundaries of orbit, anterior cranial fossa superiorly, and nasal cavities inferiorly.
Structure  Cribriform plate - forms roof of nasal cavity
Two ethmoidal labyrinths - contain ethmoidal cells and ethmoidal sinus
Perpendicular plate
- forms nasal septum
Borders Anteriorly: frontal bone
Posteriorly: sphenoid bone
Inferiorly: vomer and inferior nasal concha
Osseous development Endochondral ossification
Contents
  1. Relations
  2. Anatomy
    1. Ethmoidal labyrinths
    2. Cribriform plate
    3. Perpendicular plate
  3. Osseous development
  4. Sources
+ Show all

Relations

The ethmoid bone is a spongy, irregular bone of the skull. It is located anteriorly in the cranial base and contributes to the formation of the medial walls of the orbit, the nasal septum, and the roof and lateral walls of the nasal cavity. Because of its central location within the skull the ethmoid bone comes in contact with 13 skull bones (e.g. frontal bone, sphenoid bone, palatine bones, maxilla, nasal bones, lacrimal bones, inferior nasal conchae, and vomer

Anatomy

The ethmoid bone consists of four major components that include: 

  • The cribriform plate;
  • Two ethmoidal labyrinths;
  • The perpendicular plate.
Ethmoid bone - labeled structures 

Ethmoidal labyrinths

The ethmoid labyrinths lie on both lateral sides and contain numerous little cavities with ethmoidal cells which comprise the ethmoidal sinus. The ethmoidal cells are important structures for the skull, responsible for olfactory sensation, humidification, phonation, and ventilation.

The labyrinths also form two of the prominent structures of 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.

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, a small vertical protrusion on top of the plate. The olfactory bulbs lie on two grooves lateral to the crista galli.

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.

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.

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