The sieve-like bone whose perforated plate lets the nerves of smell pass from the nose to the brain
Ethmoid bone — the cribriform plate transmits olfactory nerve fibres (from the Greek ethmos, sieve).
Anatomy · Bones
Ethmoid bone
The sieve bone
Skull · cranium and nose
The ethmoid is a small, light, spongy, unpaired bone at the midline of the front of the cranium, between the two orbits and above the nose. It forms part of the roof and side walls of the nasal cavity, the upper nasal septum and the inner wall of the eye socket. Its sieve-like plate lets the olfactory nerve fibres pass up from the nose.
How to spot them
- ▸A small, delicate, cube-like bone deep in the midline between the eyes, roofing the nose
- ▸A horizontal sieve-like plate, with a cockscomb-shaped crest projecting upwards
- ▸A vertical plate hangs down as the upper part of the nasal septum
- ▸Two labyrinths, one on each side, filled with air cells and forming the nasal conchae
What to know
A small upward projection at the midline, named for a cockerel's comb, anchors the falx cerebri
Ethmoid bone — the crista galli.
Its downward plate forms the upper part of the nasal septum, with the vomer below
Ethmoid bone — the perpendicular plate.
Paired masses at either side of the nose contain many air cells and give rise to the superior and middle conchae
Ethmoid bone — the ethmoidal labyrinths.
A blow to the nose can fracture its perforated plate, causing loss of smell or a clear watery leak of cerebrospinal fluid from the nostril
Ethmoid bone — anosmia and CSF rhinorrhoea.
Its paper-thin orbital plate forms the medial wall of the eye socket, so infection of its sinuses can spread into the orbit
Ethmoid bone — the lamina papyracea separates the ethmoidal air cells from the orbit.
It lies between the two orbits and forms part of the anterior cranial fossa's floor, articulating with thirteen other bones
Ethmoid bone — nasal, maxillae, lacrimal, palatine and inferior conchae (paired); frontal, vomer and sphenoid (unpaired).
Key ideas
- Three parts: the cribriform plate (roof of the nose, with the crista galli above), the perpendicular plate (upper septum) and the two ethmoidal labyrinths (air cells).
- The ethmoidal air cells are among the paranasal sinuses and drain into the nasal cavity.
Quick-fire facts
- •One of the 8 cranial bones, but it also contributes to the face, since it forms part of the nasal cavity and orbit
- •The olfactory nerve (cranial nerve I) fibres pass through the cribriform plate
- •The crista galli anchors the falx cerebri; its name is Latin for cock's comb
- •The perpendicular plate forms the upper part of the nasal septum (about the upper two-thirds by TeachMeAnatomy's account) and the vomer forms the lower part
- •The superior and middle nasal conchae are outgrowths of the ethmoid; the inferior concha is a separate bone
- •Fractures of the labyrinth may allow air from the nose to enter the orbit (orbital emphysema)
- •Common causes of ethmoid fracture include facial trauma such as hitting the dashboard, or a fall from a height
- •It is lightweight and spongy, hence the name from the Greek ethmos, sieve
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Sources
- TeachMeAnatomy — The Ethmoid Bone
- OpenStax — Anatomy and Physiology 2e, 7.2 The Skull