146 



HUMAN PHYSIOLOGY 



of the tympanic membrane. The ear is functioning 

 as an aneroid barometer. 



The tympanic membrane is adapted to vibrate freely in 

 response to a wide range of vibrations in the air which 

 comes into contact with it. It is much more serviceable 

 than it could be if it had a strong tendency to take up 

 a fixed rate of tremor. In other words, it has little 



Spiral 

 ganglion. 



Osseous cod dear wall. Nervus cochlearis. 



FIG. 33. Longitudinal section of the cochlea of a cat. This figure 

 gives a general view of the cochlea. The cochlear duct is met with six 

 times in the section. (Sobotta.) 



resonance. Attached to the membrane on its inner 

 surface is a minute bone or ossicle which must vibrate 

 with it. This ossicle transmits its motion to a second 

 and this, in turn, to a third. The three articulated 

 bones convey the vibrations, without altering their 

 frequency, across the tympanum and to the beginning 

 of the internal ear. 



The third ossicle is fitted into an opening which is 



