THE SENSE ORGANS 175 



Place first the right side and then the left side of your head flat 

 against a pillow. Do you hear the sounds of your heart? In which 

 ear are they perceived most clearly? Give an explanation of this 

 phenomenon. 



15. Compound Tones. Set in vibration a violin string fixed be- 

 tween two points. Touch the center of the string with a rod. Observe 

 that the original fundamental tone is now obliterated, the lowest tone 

 being an octave higher. 



16. Observation of the Membrana Tympani in Man. Fasten the 

 reflector to your forehead, and direct the rays from a lantern into the 

 right external auditory meatus of the subject. With your left hand pull 

 the external ear backward and upward, and with your right hand insert 

 the funnel-shaped tube, taking great care not to injure the skin of the 

 meatus or the membrana tympani. Concentrate the light upon this 

 membrane by moving the reflector either nearer to or farther away from 



Membrana flaccida Posterior ligament 



Anterior UgameniW jg HBpfe-Lonq process of incus 



- End of manubrium of malleus 



FIG. 101. MEMBRANA TYMPANI, AS SEEN WITH THE OTOSCOPE. (Heusman.) 



the ear. Adjust the tube by tilting it, so that a view of the entire 

 membrane may be had. The light should be placed about 60 cm. from 

 the reflector, and the reflector about 17 cm. from the membrane. 



Near the upper anterior border of the membrane will be seen the 

 short process of the malleus, the handle of the malleus extending down- 

 ward and backward from the short process. Locate the "umbo," 

 which is the most retracted area of the membrane, and identify the 

 "pars flaccida," the "pars tensa," and the "annulus cartilagineus." 



17. Pressure in the Tympanum. Close the mouth and nostrils. 

 Attempt to inspire, and swallow. Note the peculiar sensation in the 

 ears and the diminution in the acuity of hearing. 



Close the mouth and nostrils. Attempt to expire, and swallow. A 

 similar sensation is produced. Show how these acts affect the pressure 

 in the tympanum and the vibratory quality of the ear drum. 



18. Models of the Middle Ear. Examine such models as may be 

 available for illustrating the action of the ossicles. 



