on the Membrana Tympani. 15 



Case 3. An eminent music master, after catching cold, found 

 a confusion of sounds in his ears. Upon strict attention, he dis- 

 covered that the pitch of one ear was half a note lower than that 

 of the other; and that the perception of a simple sound did not 

 reach both ears at the same instant, but seemed as two distinct 

 sounds, following each other in quick succession, the last being 

 the lowest and weakest. This complaint distressed him for 

 a long time, but he recovered from it without any medical 

 aid. 



In this case, the whole defect appears to have been in the 

 action of the radiated muscle, exerted neither with the same 

 quickness nor force in one ear as in the other, so that the sound 

 was half a note too low, as well as later in being impressed 

 upon the organ. 



This affection of the muscle of the membrana tympani is 

 very similar to an affection of the straight muscles of one of 

 the eyes, producing double vision, which I have noticed in a 

 former lecture, when treating of the wrong actions of that 

 organ.* 



In endeavouring to explain the uses of the more internal parts 

 of the ear, considerable advantage may be derived from class- 

 ing them in two divisions ; namely, those which are formed for 

 the purpose of receiving impressions conveyed through the me- 

 dium of liquid or of solid substances ; and those adapted to re- 

 ceive impressions made by the impulses of an elastic fluid, as 

 the common air. 



This can be done very correctly. Fish, which are formed to 

 hear in water, can have only the parts belonging to the first 

 division; while all the parts found in the ears of birds and 



* Vide Philosophical Transactions for the year 1797. 



