NASAL FOSSJ3 AND SINUSES OF THE NOSE. 29 



floor, internal wall, external wall, and the anterior and 

 posterior nares. The vertical diameter of the nasal fossae 

 is greater at the middle of the cavities than at the an- 

 terior or posterior parts, and the transverse diameter 

 greater below than above. 



The roof is formed by the nasal bones, the nasal spine 

 of the frontal, the cribriform plate of the ethmoid, and 

 the body of the sphenoid. It is to be noted that the 

 entire roof is not horizontal, the cribriform plate only 

 being so, and that it slopes downwards at front and 

 back. 



The floor is formed by the palate plates of the superior 

 maxillary and palate bones. 



The internal wall or septum is formed chiefly by the 

 perpendicular plate of the ethmoid and by the vomer ; 

 the septal plane is further assisted by the nasal spine 

 of the frontal, the crests of the nasal, superior maxilla, 

 and palate bones. (The septum is rendered complete by 

 the triangular cartilage, which projects forwards, assist- 

 ing in giving shape and prominence to the nose.) 



The outer wall is divided into the three meatuses by 

 the projection from it of the three turbinated bones. It 

 is formed by the nasal, the superior maxillary, the lat- 

 eral mass of the ethmoid, and the lachrymal bones ; pos- 

 teriorly by the ascending plate of the palate, and the in- 

 ternal pterygoid plate of the sphenoid ; the wall is com- 

 pleted by the lateral cartilages. 



Meatuses. The outer wall of each fossa is subdivided 

 into three (sometimes four) irregular channels, termed 

 rneatuses viz., superior, middle, and inferior. The 

 bones entering into the formation of these meatuses are 

 all those of the face, excepting the malar and inferior 

 maxilla. 



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