154 



THE SENSES. 

 FIG. 42. 



Distribution of Nerves in the Nasal Passages: 1, olfactory bulb, with its nerves; 2, nasal 

 branch of the fifth pair ; 3, spheno-palatine ganglion. 



special end-organs, known as olfactory cells, which lie under the 

 ciliated epithelium of the part. 



Describe the origin of the olfactory nerves. 



The nerves arise from a mass of gray matter lying beneath the 

 anterior lobe of the brain upon the cribriform plate of the ethmoid 

 bone. This is the olfactory bulb, and it is connected by the 

 olfactory tract with the cerebrum. 



Is tactile sensibility a property of the olfactory nerve ? 



No. The lining membrane of the nasal cavity is very sensitive 

 to irritation, but the nasal branch of the fifth nerve and branches 

 from the spheno-palatine ganglion furnish the ordinary and tactile 

 sense. 



Do the perceptions by the olfactory and by the nerves of touch 



resemble each other? 



Often they do, and some stimuli affect both nerves. The com- 

 mon sensibility is evoked by such substances as are irritating and 

 acrid : ammonia gas has no odor, but it stimulates the mucous mem- 

 brane by its irritating properties. The tactile or common sensibil- 

 ities remain when the olfactory are gone. The relation between 



