126 PHYSIOLOGY FOR THE LABORATORY. 



III. THE INTERNAL EAR, OR LABYRINTH. 



The Internal Ear, or Labyrinth, is protected by the 

 temporal bone of the skull. 



a. The vestibule is the middle part. 



b. The semicircular canals are on one side of the ves- 

 tibule. 



c. The cochlea, a spirally coiled tube, is on the opposite 

 side of the vestibule. 



IV. THE PATH or THE SOUND WAVES. 



Trace the path of the sound waves through the drum, 

 the tympanic bones, the liquids in the labyrinth to the 

 auditory nerve. 



B. A Test for Hearing. 

 Apparatus. A watch. 



a. Sit in a chair and have some one hold a ticking 

 watch at the side of one ear. How far can the watch be 

 carried before it ceases to be audible? Test the other 

 ear to see if it is equally acute. 



b. Hold a ticking watch between the teeth and notice 

 how loud it ticks. Close both ears and notice the result. 

 Repeat and uncover one ear. 



C. Location of Sound. 

 Apparatus. Two rods of iron to make a distinct sound. 



Blindfold a person and see how well sounds in front, 

 at the back, and at the sides may be located. 



