COMPARATIVE PHYSIOLOGY OF HEARING. 193 



whole the more perfect, and we may presume therefore, 

 that such is the case with respect to the ear. 



It does 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 hearing are required, since Sir Astley Cooper has 

 recorded cases in which hearing remained perfect, after 

 the tympanum was destroyed, and the little bones lost. 

 More commonly, however, the loss of these parts pro- 

 duce total deafness for a time, after which, the power 

 of hearing is often in a measure regained, and in some 

 instances entirely. 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. 



We have seen that the organs of Circulation, of Vis- 

 ion, 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 

 perfection, as animals rise in the scale of capacity and 

 power. 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 nor bones, nor indeed 

 any of the complex accessory parts found in the mam- 

 malia and man. 



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 to 



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

 ing 1 What effect does the puncture of the ear-drum have upon the 

 hearing 1 What is said of the continuation of the auditory organs in the 

 lower and higher orders of animals 1 What does the organ of hearing in 

 fishes consist of? 



17 



