FUNCTIONS OF THE MIDDLE EAR. 537 



of the labyrinth. This peculiar property of membranes is the 

 result, not of their tenuity alone, but of the elasticity and ca- 

 pability of displacement of their particles ; and it is not im- 

 paired when, like the membrane of the fenestra rotunda, they 

 are not impregnated with moisture. 



Sonorous vibrations are also communicated without any per- 

 ceptible loss of intensity from the air to the water, when to 

 the membrane forming the medium of communication, there 

 is attached a short, solid body, which occupies the greater part 

 of its surface, and is alone in contact with the water. This 

 fact elucidates the action of the fenestra ovalis, and of the 

 plate of the stapes which occupies it, and, with the preceding 

 fact, shows that both fenestrse that closed by membrane only, 

 and that with which the movable stapes is connected trans- 

 mit very freely the sonorous vibrations from the air to the fluid 

 of the labyrinth. 



A small, solid body, fixed in an opening by means of a 

 border of membrane, so as to be movable, communicates sonor- 

 ous vibrations from air on the one side, to water, or the fluid 

 of the labyrinth, on the other side, much better than solid 

 media not so constructed. But the propagation of sound to 

 the fluid is rendered much more perfect if the solid conductor 

 thus occupying the opening, or feiiestra ovalis, is by its other 

 end fixed to the middle of a tense membrane, which has atmos- 

 pheric air on both sides. 



A tense membrane is a much better conductor of the vibra- 

 tions of air than any other solid body bounded by definite 

 surfaces: and the vibrations are also communicated very 

 readily by tense membranes to solid bodies in contact with 

 them. Thus, then, the membrana tympani serves for the trans- 

 mission of sound from the air to the chain of auditory bones. 

 Stretched tightly in its osseous ring, it vibrates with the air in 

 the auditory passage, as any thin tense membrane will when 

 the air near it is thrown into vibrations by the sounding of a 

 tuning-fork or a musical string. And, from such a tense vi- 

 brating membrane, the vibrations are communicated with great 

 intensity to solid bodies which touch it at any point. If, for 

 example, one end of a flat piece of wood be applied to the 

 membrane of a drum while the other end is held in the hand, 

 vibrations are felt distinctly when the vibrating tuning-fork is 

 held over the membrane without touching it ; but the wood 

 alone, isolated from the membrane, will only very feebly propa- 

 gate the vibrations of the air to the hand. 



The ossicula of the ear, which are represented in this experi- 

 ment by a piece of wood, are the better conductors of the so- 

 norous vibrations communicated to them, on account of being 



