COMPARATIVE PHYSIOLOGY OF HEARING. 189 



whole the more perfect, and we may presume, therefore, 

 that such is the case with respect to the ear. 



585. It dots not, however, appear, that the preliminary 

 steps with respect to the introduction of sonorous vibra- 

 tions into the ear, as above described, are necessary ; nor 

 that all the parts usually concerned in the process of hear- 

 ing are required, since Sir Astley Cooper has recorded 

 cases in which hearing remained perfect, after the tympa- 

 num was destroyed, and the little bones lost. More com- 

 monly, however, the loss of these parts produce total 

 deafness for a time, after which the power of hearing is 

 often, in a measure, regained, and in some instances entire- 

 ly. It is well known, that a puncture through the ear- 

 drum does not at all affect the power of that organ. 



COMPARATIVE PHYSIOLOGY OF HEARING. 



586. We have seen that the organs of circulation, of 

 vision, and of respiration and digestion, all present the 

 most simple structures in the lower orders of animals, 

 and that all these organs increase in complexity and per- 

 fection, as animals rise in the scale of. capacity and pow- 

 er. The organs of hearing follow the same law of 

 gradation, the most complex being found in the higher 

 orders of animals, of which we have an example in 

 those of man. In the inferior races, hearing is perform- 

 ed by means of a simple vestibule with its membranous 

 sac, supplied with nervous filaments leading through the 

 auditory nerve to the brain. This simple form is found 

 in most aquatic animals, the sonorous undulations of the 

 water requiring neither tympanum or bones, nor indeed 

 any of the complex accessory parts found in the mammalia 

 and man. 



587. We have seen, that, according to the experiment 

 of Franklin, sound passes to a great distance through 

 water without losing much of its intensity, and, according 



What effect does, the destruction of the ear-drum have upon the hear- 

 ing ? What effect does the puncture of the ear-drum have upon the hear- 

 ing? What is said of the continuation of the auditory organs in the 

 lower and higher orders of animals ? What does the organ of hearing in 

 fishes consist of 



