THE SPECIAL SENSES. 



221 



or drum of the ear, in like manner has an opening by 

 means of which it communicates freely with the external 

 air. This opening is a narrow canal, about an inch and a 

 half long, called the Eustachian tube, after the name of its 

 discoverer, Eustachius. _^. 



98. The course of this passage is indicated in Fig. 54, i, 

 directed downward and inward: its other extremity opens 

 into the upper part of the throat. The passage itself is 



FIG. 54. SECTION or THE RIGHT EAR. 



A, The Concha. E, Incus, or Anvil. 



B, Auditory Canal. M, Malleus, or Mallet. 



C, Membrane of the Drum, I, Eustachian Tube. 



(the lower half.) - G, Semicircular Canals. 



D, A small muscle. H, Cochlea, or snail's shell. 



ordinarily closed, but whenever the act of swallowing or 

 gaping takes place, the orifice in the throat is stretched 

 open, and the air of the cavity of the tympanum may then 

 be renewed. Air may at will be made to enter through 

 this tube, by closing the mouth and nose, and then trying 



98. What can you state of the action of the Eustachian tube ? 



