SYSTEMATIC ANALYSIS OF APPARATUS. 



ganglia, and the mind will perceive all the sensations of 

 sound, which are called feeble, loud; sweet, rough; low, 

 high; and by a thousand other names expressive of dif- 

 ferent degrees of force, quality, and pitch. 



177. THE EAR, or Organ of Sense of Hearing, is 

 constituted of three parts, called the external, middle, 

 and internal ear. 



FIG. 73. 



Fig. 73 is a, beautiful view of 

 the Ear; 1, external, 2, mid- 

 dle, 3, inner ear ; 13, a sec- 

 tion of the air-tube, which sec- 

 tion extends through the front 

 of 2, and the middle of 19, a 

 tube called Eustachian, lead- 

 ing to back part of nostril. If 

 a person close the nose and 

 mouth, and blow air from the 

 lungs, it will press up that 

 tube into 2, and produce a 

 ringing. 14, bottom of air- 

 tube, a tremulous membrane 

 that, acting on nerves, deter- 

 mines/era? ; 22, semi-circular 

 canals, that determines quali- 

 ty ; 24, cochlea, that deter- 

 mines pitch ; 18, bones of ear. 



178. THE EXTERNAL EAR is adapted to receive a 

 wave of air and transmit it to 



179. THE INTERNAL EAR, COMPOSED of three parts, 

 each acted upon by its corresponding influence, and con- 

 nected by nerves with Ganglia. If all these parts are 

 perfect, correct sensations of the three kinds will be 

 produced ; but if one should be imperfect by constitution 

 or by disease, the sensations of that class will be imperfect 

 or wanting. Thus a person may have correct ideas of 

 the force of a sound and not of its pitch, &c., as is not 

 unfrequently the case. The ears may be unlike, and 



177. how divided ? Describe Fig. 73. 178. how adapted ? 179. How ? 

 May a person have correct sensations of one class and not of the other? 



