310 ANIMAL BIOLOGY 



membrane lies the space called the middle ear. This is 

 connected with the pharynx by the Eustachian tube which 

 serves to admit air to the middle ear from the throat. 

 When one swallows one can usually hear the opening of 

 this tube. 



Connected with the drum membrane on the one side 

 and with the inner ear on the other is a chain of three small 

 bones, called the hammer, the anvil, and the stirrup. 

 Sound waves set the drum membrane into vibrations 

 which are conveyed by these bones to the inner ear where 

 they stimulate the end organs of the auditory nerve. 

 The inner ear is a delicate, complex structure lodged in a 

 cavity within the bones of the .skull. The spirally wound 

 cochlea which resembles a snail shell in shape contains the 

 delicate end organs of the nerves of hearing. Another 

 part of the internal ear consisting of three semicircular 

 canals has a very different function, as it forms an organ 

 for the maintenance of the equilibrium of the body. 



