SMELL. 



489 



perceive the existence of an odorous substance at a distance, and 

 when it is altogether concealed from sight. The minute quantity 

 of volatile material emanating from it, and thus pervading the 

 atmosphere, comes in contact with the mucous membrane of the 

 nose, and produces a peculiar and special sensation. 



The apparatus of this sense consists, first, of the olfactory mem- 

 brane, supplied by the filaments of the olfactory nerve, as its 

 special organ ; and secondly, of the nasal passages, with the tur- 

 binated bones and the muscles of the anterior and posterior nares, 

 as its accessory organs. At the upper part of the nasal fossae, 

 the mucous membrane is very thick, soft, spongy and vascular, 

 and is supplied with mucous follicles which exude a secretion, by 

 which its surface is protected and kept in a moist and sensitive 

 condition. 



It is only this portion of the mucous membrane of the nares 

 which is supplied by filaments of the olfactory nerve, and which is 

 capable of receiving the impressions of smell ; it is therefore called 

 the Olfactory membrane. Elsewhere, the nasal passages are lined 

 with a mucous membrane which is less vascular and spongy in 

 structure, and which is called the Schneiderian membrane. 



The filaments derived from the olfactory ganglia, and which 

 penetrate through the cribri- 

 form plate of the ethmoid 

 bone, are distributed to the 

 mucous membrane of the su- 

 perior and middle turbinated 

 bones, and to that of the upper 

 part of the septum nasi. The 

 exact mode in which these 

 filaments terminate in the ol- 

 factory membrane has not 

 been definitely ascertained. 

 They are of a soft consistency 

 and gray color, and, after di- 

 viding and ramifying freely 

 in the membrane, appear to 

 become lost in its substance. 

 It is these nerves which exer- 

 cise the special function of 

 smell. They are, to all appearnnce, incapable of receiving ordinary 

 impressions, and must be regarded as entirely peculiar in their 



DISTRIBUTION OF XEKVE s IN THE NASAI. 

 FASSJAUES. 1. Olfactory ganglion, w'thits nerves 

 2. Nasal branch of fifth pair. 3. Spheuo-palatiue 

 ganglion. 



