534 THE SENSE OF HEARING. 



the nerves are arranged in a plexus, containing ganglion cells. 

 Their ultimate termination is not known with certainty ; but 

 some of them, without doubt, end in the organ of Corti, prob- 

 ably in cells. 



Physiology of Hearing. 



The acoustic portion of the physiology of hearing is thus il- 

 lustrated by Miiller: chiefly in applications of the results of 

 his experiments on the conduction of sonorous vibrations 

 through various combinations of air, water, and solid sub- 

 stances, especially membrane. 



All the acoustic contrivances of the organ of hearing are 

 means for conducting the sound, just as the optical apparatus 

 of the eye are media for conducting the light. Since all mat- 

 ter is capable of propagating sonorous vibrations, the simplest 

 conditions must be sufficient for mere hearing ; for all sub- 

 stances surrounding the auditory nerve would communicate 

 sound to it. In the eye a certain construction was required 

 for directing the rays or undulations of light in such a man- 

 ner that they should fall upon the optic nerve with the same 

 relative disposition as that with which they issued from the 

 object. In the sense of hearing this is not requisite. Sonorous 

 vibrations, having the most various direction and the most 

 unequal rate of succession, are transmitted by all media with- 

 out modification, however manifold their decussations ; and, 

 wherever these vibrations or undulations fall upon the organ 

 of hearing and the auditory nerves, they must cause the sensa- 

 tion of corresponding sounds. The whole development of the 

 organ' of hearing, therefore, can have for its object merely the 

 rendering more perfect the propagation of the sonorous vibra- 

 tions, and their multiplication by resonance ; and, in fact, all 

 the acoustic apparatus of the organ may be shown to have 

 reference to these two principals. 



Functions of the External Ear. 



The external auditory passage influences the propagation of 

 sound to the tympanum in three ways : 1, by causing the 

 sonorous undulations, entering directly from the atmosphere, 

 to be transmitted by the air in the passage immediately to the 

 membrana tympani, and thus preventing them from being 

 dispersed ; 2, by the walls of the passage conducting the so- 

 norous undulations imparted to the external ear itself, by the 

 shortest path to the attachment of the membrana tympani, 

 and so to this membrane ; 3, by the resonance of the column 

 of air contained within the passage. 



