The Senses a 
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 
Fic. 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- 
