OS ETHMOIDES. 77 



the upper channel or meatus of the nose. The edge of the 

 surface immediately above it projects in a small degree over 

 this channel or groove ; having been described by Morgagni, it 

 bears his name, and may be considered as one of the"~^pongy 

 or turbinated bones ; from its situation, it should be called the 

 first or superior. The groove is very deep, and most of the cells 

 of the posterior part of the ethmoid bone communicate with it, 

 through one or more foramina at its anterior extremity. 



The part of the surface of the ethmoid which is immediately 

 below this groove, is convex ; that which is before and below 

 it, is rather flat ; the convex part is the middle spongy or 

 turbinated bone, as it has commonly been called ; it projects 

 obliquely into the cavity of the nose, and hangs over the middle 

 channel or meatus, which is immediately below the ethmoid 

 bone. The internal surface of this spongy bone, which is 

 opposite the septum of the nose, is convex and rough or spongy ; 

 the external surface is concave. The anterior cells of the 

 ethmoid, and particularly those which the frontal sinuses on 

 each side communicate with, open into the middle channel or 

 meatus, under the anterior end of this turbinated bone. 



This middle channel or meatus, is much larger than that 

 above ; it extends from the anterior to the posterior part of the 

 nostrils, and slopes downwards and backwards. The cavity of 

 the upper maxillary bone, or the antrum highmorianum, opens 

 on each side into this meatus, and a thin plate of bone extends 

 from the cellular part of the ethmoid so as to cover a part of it. 



The cellular portions of the ethmoid are composed of plates 

 thinner than the shell of an egg ; they are entirely hollow, and 

 the cells are very various, in number, size, and shape. Some 

 cells of the uppermost row communicate with those of the 

 os frontis, formed by the separation of the plates of the orbitar 

 process of that bone. 



From the posterior part of the cribriform plate, where it is 

 in contact with the lesser wings of the sphenoidal bone, thin 

 plates of bone pass down upon the anterior surface of the body 

 of the os sphenoides, one on each side of the azygos process, 

 and often diminish the opening into the sphenoidal cells. 

 These plates are sometimes triangular in form, the basis uniting 

 7* 



