632 THE SENSE OF SMELL. 



odorous matter should be transmitted in a current through 

 the nostrils. This is effected by an inspiratory movement, 

 the mouth being closed ; hence we have voluntary influence 

 over the sense of smell ; for by interrupting respiration 

 we prevent the perception of odours, and by repeated quick 

 inspirations, assisted, as in the act of sniffing, by the action of 

 the nostrils, we render the impression more intense (see 



P- 2 35)- 



The human organ of smell is essentially formed by the 

 filaments of the olfactory nerves, distributed in minute 

 Fig. 169.* 



arrangement, in the mucous membrane covering the upper 

 third of the septum of the nose, the superior turbinated or 

 spongy bone, the upper part of the middle turbinated bone, 

 and the upper wall of the nasal cavities beneath the cribri- 

 form plates of the ethmoid bone (figs. 169 and 170). 

 This olfactory region is covered by cells of cylindrical epi- 



* Fig. 169. Nerves of the septum nasi, seen from the right side (from 

 Sappey after Hirschfeld and Leveille). . I, the olfactory hulb ; I, the 

 olfactory nerves passing through the foramina of the cribriform plate, 

 and descending to he distributed on the septum ; 2, the internal or septal 

 twig of the nasal branch of the ophthalmic nerve; 3, naso-palatine 

 nerves. 



