CorpusHuman Anatomy
SkeletalBone

Ethmoid bone

Os ethmoidale

A light, cuboidal, spongy bone between the orbits that forms the roof of the nasal cavity (cribriform plate), the upper nasal septum, the superior and middle nasal conchae and the ethmoidal air cells.

Show on body map Skull — Lateral View Smell and Taste — Chemoreceptors

Overview

The ethmoid consists of a horizontal cribriform plate, a vertical perpendicular plate and two ethmoidal labyrinths suspended from the cribriform plate. The cribriform plate, perforated by ≈20 foramina for the olfactory nerve filaments, sits in the ethmoidal notch of the frontal bone; projecting upward from it is the crista galli, attaching the falx cerebri. The perpendicular plate descends to form the upper part of the nasal septum, articulating with the vomer and septal cartilage.

Each labyrinth contains the ethmoidal air cells (anterior, middle and posterior groups) — a honeycomb of sinuses. Its lateral wall, the orbital plate (lamina papyracea), is paper-thin and forms most of the medial wall of the orbit. Its medial surface carries the superior and middle nasal conchae; below the middle concha lie the ethmoidal bulla, uncinate process and the semilunar hiatus into which the frontal and maxillary sinuses and anterior ethmoidal cells drain (the ostiomeatal complex). The anterior and posterior ethmoidal foramina at the frontoethmoidal suture transmit the corresponding nerves and vessels.

Location

Anterior cranial base between the orbits; roof and lateral walls of the upper nasal cavity.

Parts & subdivisions

  1. Cribriform plate
    Perforated roof of the nasal cavity transmitting olfactory nerve filaments (CN I).
  2. Crista galli
    Midline crest anchoring the falx cerebri.
  3. Perpendicular plate
    Superior part of the bony nasal septum.
  4. Ethmoidal labyrinths and air cells
    Anterior, middle and posterior cells draining into the middle and superior meatuses.
  5. Orbital plate (lamina papyracea)
    Thin medial orbital wall.
  6. Superior and middle nasal conchae
    Scroll-like projections increasing nasal mucosal surface area.
  7. Uncinate process and ethmoidal bulla
    Bound the semilunar hiatus in the middle meatus.

Anatomy

Articulations

Frontal, sphenoid, nasal bones, maxillae, lacrimal bones, palatine bones, inferior nasal conchae and vomer.

Ossification

Endochondral, from three centres (one per labyrinth prenatally and one for the perpendicular plate in the first year); parts unite by ≈3 years.

Function

  • Separates the nasal cavity from the anterior cranial fossa
  • Transmits olfactory nerves to the olfactory bulbs
  • Forms the medial orbital walls, upper nasal septum and lateral nasal walls
  • Warms and humidifies air via conchae; lightens the skull via air cells

Clinical significance

Cribriform plate fracture

Anterior skull-base fracture → CSF rhinorrhoea (glucose/β2-transferrin positive), anosmia and risk of meningitis.

Orbital cellulitis from ethmoiditis

Infection crosses the thin lamina papyracea — the commonest cause of orbital cellulitis in children (proptosis, painful ophthalmoplegia, reduced acuity).

Medial blow-out fracture

Lamina papyracea fracture may entrap the medial rectus and cause orbital emphysema after nose-blowing.

Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.