California State University, Chico

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Text, Layout, and Graphics Copyright © 1995 by Turhon Murad
Design, and Graphics Copyright © 1995 by Nanci Ellis

Project was sponsored, in part, by Technology and Learning Program, CSU, Chico

The Ethmoid

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If the sphenoid is the most difficult cranial bone to describe and invision, the Ethmoid is the second most difficult. It has a number of features and projections, but unlike the sphenoid it cannot be seen from various views of the skull. Like the sphenoid, it is a single bone that runs through the mid-sagittal plane and aids to connect the cranial skeleton to the facial skeleton. It consists of various plates and paired projections. The most superior projection is the Crista Galli, or Cocks Comb, found within the cranium. It assists in dividing the left and right frontal lobes of the brain. Lateral projections from the Crista Galli are the left and right Cribriform Plates which in life cradle the first cranial nerves i.e., the olfactory nerves. The nerves brachiate through the porosity of these plates into the nasal cavity below. Directly inferior to the Crista Galli and running in the mid-sagittal plane is the Perpendicular Plate of the ethmoid which articulates with the vomer more inferiorly and assists in separating the left and right nasal passages. The Perpendicular Plate can be viewed anteriorly through the nasal cavity.

Descending off each of the Cribriform Plates is a left or right Orbital Plate which aids to form the medial wall of the respective eye orbit. Each Orbital Plate is rectangular in shape and gives rise to two medial projections, the Superior and Middle Nasal Concha. These projections, like the separate Inferior Nasal Concha, assist in increasing the surface area within the nasal cavity and thereby the exposure of the brachiating olfactory nerve to inhaled odors. The Superor or Supreme Nasal Conche are smaller, and cannot be viewed through the anterior nasal opening because it is blocked from view by the the more inferior Middle Nasal Conche.

The ethmoid touches, or articulates with, the following bones:

Glossary

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Last Updated: Jan. 24, 2000