The Senses 



217 



Two membranes are stretched across the ear-tube, 

 and between these a tiny bone, the columella, is sus- 

 pended, taking the place of the chain of three bones in 

 the ear of a mammal. When sound-waves strike against 

 the outermost membrane, or drum of the ear, vibrations 

 are transmitted by the little bony suspension bridge to 

 the inner membrane, and this in turn troubles the fluid 



FIG. 157. External ear of Barred Owl. 



which fills the inner ear. The hair-like endings of the 

 nerve of hearing are affected by the vibrations of the 

 fluid and thus is hearing accomplished. Rather say, 

 thus the disposition of the physical components of the 

 ear may be explained; but how anything more than the 

 monotone of a sea-shell's cavity is translated to the brain, 

 no one can say. 



The fluid contained in three semicircular canals, situ- 



