56 Royal Society :— 
«On the Mode in which Sonorous Undulations are conducted from 
the Membrana Tympani to the Labyrinth, in the Human Ear.” By 
Joseph Toynbee, Esq., F.R.S. &c. 
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 condct 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 ossiculat+;”’ 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 
conseguence hangs loose, deafness does not follow f.” 
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 
nearly total deafness ; and the following experiments, which demon- 
strate the great facility with which sonorous undulations pass from 
the air to a solid body, indicate that the stapes, even when isolated 
from the other bones of the chain, may still be a medium for the 
transmission of sound. 
Experiment 1.—Both ears having been closed, a piece of wood, 
5 inches long and half an inch in diameter, was held between the 
teeth, and a vibrating tuning-fork C’ having been brought within 
the eighth of an inch of its free extremity, the sound was heard 
distinctly, and it continued to be heard between five and six seconds. 
Leperiment 2.—One end of the piece of wood used in the pre- 
vious experiment being pressed against the tragus of the outer ear, so 
as to close the external meatus without compressing the air con- 
* Mr. Wharton Jones, Cyclopzdia of Surgery, Art. “ Diseases of the Ear,” 
p- 23. 
+ Lancet, 1843, p. 380. 
} Encyclopedia Metropolitana, Art. ‘ Sound,” p. 810. 
