V. "On the Mode in which Sonorous Undulations are con- 

 ducted from the Membrana Tympani to the Labyrinth, in 

 the Human Ear." By JOSEPH TOYNBEE, Esq., F.E.S. &c. 

 Received May 24, 1859. 



The opinion usually entertained by physiologists is that two 

 channels are requisite for the transmission of sonorous undulations 

 from the membrana tympani to the labyrinth, viz. the air in the 

 tympanic cavity which transmits the undulations to the membrane 

 of the fenestra rotunda and the cochlea ; and secondly, the chain of 

 ossicles which conduct them to the vestibule. 



This opinion is, however, far from being universally received ; 

 thus, one writer on the Physiology of Hearing contends that " the 

 integrity of one fenestra may suffice for the exercise of hearing*;" 

 another expresses his conviction that " the transmission of sound 

 cannot take place through the ossiculaf;" while Sir John Herschel, 

 in speaking of the ossicles, says " they are so far from being essential 

 to hearing, that when the tympanum is destroyed and the chain in 

 consequence hangs loose, deafness does not follow J." 



The object of this paper is to decide by experiment how far 

 the ossicles are requisite for the performance of the function of 

 hearing. 



The subject is considered under two heads, viz. 



1. Whether sonorous undulations from the external meatus can 

 reach the labyrinth without having the ossicles for a medium. 



2. Whether any peculiarity in the conformation of the chain of 

 ossicles precludes the passage of sonorous undulations through it. 



1. Can sonorous undulations reach the labyrinth from the 

 external meatus without the aid of the ossicles ? 



This question has often been answered in the affirmative, appa- 

 rently because it has been ascertained that in cases where two bones 

 of the chain of ossicles have been removed by disease, the hearing 

 power is but slightly diminished. In opposition to this view, it 

 must, however, be remembered, that the absence of the stapes, or 

 even its fixed condition (anchylosis), is always followed by total or 



* Mr. Wharton Jones, Cyclopaedia of Surgery, Art. " Diseases of the Ear," 

 p. 23. 



t Lancet, 1843, p. 380. 

 J Encyclopaedia Metropolitana, Art. " Sound," p. 810. 



