THE SPECIAL SENSES. 129 



In each half of the cavity are three small and very spongy 

 bones, curved so as to form nearly parallel ridges, and making 

 three distinct passages in each nasal cavity. (Fig. 22, p. 65.) 

 The filaments of the olfactory nerve are spread out on the 

 two upper ridges, but not on the lower. It will be seen from 

 this that the sense of smell resides chiefly in the upper part of 

 the cavity, and hence the necessity for taking an extra sniff 

 when we want to detect a very faint odor. This extra sniff 

 sends some of the air through the higher passages. 



The mucous membrane of the nose lines all its passages, 

 and is continuous with the lining of the pharynx and wind- 

 pipe. This is the most natural and healthy course for the 

 air in breathing, because the several passages or warming 

 chambers in the nose temper the air as it is drawn in, while 

 at the entrance to the nostrils small hairs grow to strain out 

 dust and other impurities from the air. 



4. Functions of the Nose. The sense of smell acts in 

 conjunction with that of taste. In fact, it precedes taste in 

 recognizing the properties of any food about to be taken into 

 the stomach. It acts a most important part in guarding 

 the portal through which the body receives its nourishment. 

 Taste seems to depend a good deal upon smell. If our sense 

 of smell is not keen, the taste is also defective. Every 

 mother knows this when she holds the nose to administer 

 a nauseous draught to her child. Sight also assists taste. 

 In fact, without the aid of sight and smell it would often 

 be impossible to distinguish substances put into the mouth. 



As stated, the lower portion of the nose takes no part in 

 detecting odors. The nerves supplied to this part are not 

 from the olfactory, but they do efficient and useful work. 

 If the air about to pass inward contains any irritating 

 substance, these nerves detect it; sneezing is induced and 

 the offending matter is forcibly expelled. The sense of smell 

 contributes largely to man's comfort and pleasure. It is ever 



