Ethmoid bone

Ethmoid bone
Sagittal section of skull. (Ethmoid bone visible as white structure to left.)
Lateral wall of nasal cavity, showing ethmoid bone in position.
Details
Identifiers
Latin	os ethmoidale
MeSH	D005004
TA98	A02.1.07.001
TA2	721
FMA	52740
Anatomical terms of bone

The ethmoid bone (from Greek ethmos, "sieve") is a bone in the skull that separates the nasal cavity from the brain. As such, it is located at the roof of the nose, between the two orbits. The cubical bone is lightweight due to a spongy construction.

Parts

The ethmoid bone consists of four parts:

• the horizontal Cribriform plate (lamina cribrosa), part of the cranial base
• the vertical Perpendicular plate (lamina perpendicularis), which is part of the nasal septum
• the two lateral masses or labyrinths.

Articulations

The ethmoid articulates with fifteen bones: four of the cranium—the frontal, the sphenoid, and the two sphenoidal chonchae; and eleven of the face—the two nasals, two maxillae, two lacrimals, two palatines, two inferior nasal conchae, and the vomer.

Injuries

The ethmoid bone is very delicate and is easily injured by a sharp upward blow to the nose, such as a person might suffer by striking an automobile dashboard in a collision. The force of a blow can drive bone fragments through the cribiform plate into the meninges or brain tissue. Such injuries are often evidenced by leakage of cerebrospinal fluid into the nasal cavity, and may be followed from the nasal cavity to the brain.

Blows to the head can also shear off the olfactory nerves that pass though the ethmoid bone and cause anosmia, an irreversible loss of the sense of smell and a great reduction in the sense of taste (most of which depends on smell). This not only deprives life of some of its pleasures, but can also be dangerous, as when a person fails to smell smoke, gas, or spoiled food.

Fracture of the lamina papyracea, the lateral plate of the ethmoid labyrinth bone, permits communication between the nasal cavity and the ipsilateral orbit through the inferomedial orbital wall, resulting in orbital emphysema. Increased pressure within the nasal cavity, as seen during sneezing, for example, leads to temporary exophthalmos.

Role in magnetoception

Main article: Magnetoception

Some birds and other migratory animals have deposits of biological magnetite in their ethmoid bones which allow them to sense the direction of the Earth's magnetic field. Humans have a similar magnetite deposit, but it is believed to be vestigial.

Additional images

• 
  The seven bones which articulate to form the orbit.
• 
  Cranial bones
• 
  Sphenoid bone visible center right.
• 
  Side view of the skull.
• 
  Medial wall of left orbit.
• 
  Base of the skull. Upper surface.
• 
  Medial wall of left nasal fossa.
• 
  Roof, floor, and lateral wall of left nasal cavity.

See also

• Ossification of ethmoid
• Bone terminology
• Terms for anatomical location

External links

• http://www.theregister.com/2006/11/17/the_odd_body_nose_compass/

This article incorporates text in the public domain from page 153 of the 20th edition of Gray's Anatomy (1918)