252 



THE SPECIAL SENSES 



which are sweet, bitter, sour, or salty, become similarly 

 tasteless. 



THE SENSE OF HEARING 



External ear. Much more complex than the mechan- 

 isms for touch, taste and smell, is that of hearing. Within 



lumnar (mucous) cell 

 factory cell 



Branching of olfactory 

 nerve fibre to 

 supply the cells 



A B 



FIG. 136. Cells from the olfactory surface : A, of the frog ; B, of man. 



each of our ears there is a small complicated structure, 

 which is sensitive to sound vibrations. Although it con- 

 tains thousands of nerve fibres and terminals, it is only 

 the size of a large pea. It is well protected by its posi- 

 tion within one of the hardest bones of the skull and 

 the sole entrance to it from without is a crooked passage, 

 the auditory canal. This canal leads from the vibration- 



