so 6 Mr. Carlisle on the Physiology of the Stapes. 
parative view exhibited in the Plate, I am led to the following 
conclusions. In man, and the most numerous orders of the 
mammalia, the figure of the stapes is an accommodation to that 
degree of lightness which, throughout the series of ossicles, 
seems a requisite condition. It is also a conductor of vibrations 
in common with the other ossicles : but most especially it is 
designed to press on the fluid contained in the labyrinth by that 
action which it receives from the stapedeus muscle, and the 
hinge-like connection of the straight side of its basis with the 
fenestra vestibuli ; the ultimate effect of which is an increase 
of the tension of the membrane closing the fenestra cochleae. 
It does not appear that any degree of motion ever subsists 
between the ossicula auditus as wholes, which bears any 
relation to the peculiar vibrations of sounds ; but rather that 
the different motions of these bones only affect the membrana 
tympani, and alter the degrees of contact in their articulations, 
so as to influence the intensity of violent impulses ; sounds of less 
impetus, not requiring such modulation, are transmitted through 
the conducting series by the vibrations of the integrant parts 
of these bones, unaccompanied by muscular action. 
This reasoning is suggested by the columellas in the aves 
and amphibia: and as many birds are known to imitate a 
variety of artificial sounds with great accuracy, it may be in- 
ferred that they hear such sounds as acutely, and with the 
same distinctness as mankind. 
It seems that all the muscles of the ossicula auditus are of 
the involuntary kind, and the peculiar stimulus to their action 
is sound. The chorda tympani, which supplies them, is a gan- 
gliated nerve : if this supposition be true, then the muscles 
should be considered as all acting together, and it is well 
