EXTENT OF THE SCHNE1DER1AN MEMBRANE. 453 



nerve. In proof of this, it is asserted that the sense of smelling 

 has entirely ceased in some cases, where the sensibility to 

 mechanical irritation of every kind has remained unchanged. 

 If the olfactory nerve alone is concerned in the function of 

 smelling it follows, that this function must be confined to the 



O' ' 



upper parts of the nasal cavities ; but it ought to be remem- 

 bered, that the structure of the Schneiderian membrane, in the 

 lower parts of these cavities, appears exactly like that which 

 is above. 



The surface of the nasal cavities and their septum, when 

 covered with the Schneiderian membrane, correspond with the 

 osseous surface formerly described. The membrane covers the 

 bones and cartilage of the septum, so as to make one uniform 

 regular surface. From the upper part of the septum, it is con- 

 tinued to the under side of the cribriform plate of the ethmoid, 

 and lines it ; the filaments of the olfactory nerve passing through 

 the foramina of that bone into the fibrous surface of the mem- 

 brane. It is continued from the septum, and from the cribri- 

 form plate, to the internal surface of the external nose, and 

 lines it. It is also continued backwards to the anterior surface 

 of the body of the sphenoidal bone ; and, passing through the 

 foramina or openings of the sphenoidal cells, it lines these 

 cavities completely ; but in these, as well as the other cavities, 

 its structure appears somewhat changed ; it becomes thinner 

 and less vascular. 



At the above mentioned foramina, in some subjects, it forms 

 a plate or fold, which diminishes the aperture considerably. 



From the upper surface of the nasal cavities, the membrane 

 is continued downwards over the surface opposite to the sep- 

 tum. On the upper flat surfaces of the cellular portions of the 

 ethmoid, it forms a smooth uniform surface. After passing over 

 the first turbinated bone, or that called after Morgagni, it is 

 reflected into the groove, or upper meatus immediately within 

 and under it ; the fold formed by the membrane, as it is reflect- 

 ed into the meatus, is rather larger than the bone : and the 

 edge of the fold therefore extends lower down than the edge 

 of the bone, and partly covers the meatus like a flap, consisting 



