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Anatomy of Skeleton 



The upper part of the vertical plate appears above the cribriform plate in one region 

 to make the strong process of the crista galli. (c) A lateral mass on each side suspended 

 from the edges of the cribriform plate and consisting of an intricate series of thin- walled 

 air cells attached to the inner aspect of a thin lateral plate termed the os planum or 

 lamina papyracea. It is this lateral mass that rests on the maxilla. The mass of air 

 cells constitute what is termed the labyrinth. 



The superior surface (Fig. 188) shows : (a) A lateral area on each side articulating 



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FIG. 188. Ethmoid. Upper figure is a scheme showing how the bone consists of a 

 central " perpendicular plate " connected above by a horizontal piece with the 

 lateral masses which rest on the maxillae, and how the outer walls of these lateral 

 masses are formed by thin laminae (os planum) which are in the inner walls of the 

 orbits. The lateral masses are composed of air-cells, from the inner walls of 

 which upper and middle turbinates are suspended and are thus connected with 

 the roof. The orbital plates of the frontal rest on the horizontal piece of the 

 ethmoid. On the right is the ethmoid seen from above, and on the left a view 

 from the right side. F,, extent of articulation with frontal ; N., with nasal bones. 



with the orbital plate of the frontal. These surfaces usually exhibit broken air cells 

 which are completed by the frontal. The anterior orbital or ethmoidal groove is 

 seen running inwards and forwards across this surface, and the posterior groove lies 

 a little behind it. 



(b) The cribriform area supports the olfactory bulbs. It is covered by dura mater, 

 under which the nasal nerves run forward from the anterior orbital grooves beside 

 the crista galli to reach a notch on each side on the front border of the bone (sometimes 

 completely closed in) in which they lie, between the ethmoid and the frontal : the 

 anterior ethmoidal arteries run with them. 



