364 STKUCTUEE OF THE DEUM. 



In this respect we may speak of it as a perfect organ ; for all mathemati- 

 cians who have written on the subject of sound agree in setting forth the 

 three peculiarities that have "been mentioned, intensity, note,' quality, as 

 the grand features of waves of sound, and this upon a mere abstract dis- 

 cussion of acoustics. Now these three essential, abstract, or theoretical 

 peculiarities of sound-waves are the very three which the organ of hear- 

 ing seizes upon, and so we are justified in saying that, in this respect, it 

 is perfect in its construction. Premising the remark that mathemati- 

 cians have abundantly proved that the intensity of sounds depends upon 

 the amplitude of excursion of the vibrating particles, and the pitch or note 

 upon wave length, I shall now proceed to offer some arguments in proof of 

 the proposition that the triple function of the ear is discharged in the fol- 

 Functionofthe l wm g wa y : 1^. That the drum is for the measurement of 

 drum, cochlea, intensity; 2d. The cochlea for the recognition of wave length; 



canals. ^ ^ Q semicircular canals for the appreciation of quality. 

 I shall endeavor to show that the ear is not a homogeneous organ, as the 

 older hypothesis supposed, but that one or other of these instrumental 

 parts may be absent, and with it will disappear its' special function, forti- 

 fying this view with facts presented by comparative anatomy, by embry- 

 onic development, and also by the relations of the voice, and showing 

 the parallel between the structure and functions of the ear, the organ for 

 normal vibrations, and of the eye, the organ for transverse ones ; and the 

 analogy and the identity of their embryonic development ; that, for in- 

 stance, the drum is the equivalent of the iris, and the cochlea of the ret- 

 ina and its adjacent parts. 



1st. On the measurement of the intensity of sound, structure of the 

 tympanic cavity or drum, and its functions. 



The tympanic cavity or drum of the ear, as we have briefly described, 

 Structure of * s an a ^ r cav ^7 ^ a cylindroid and flattened shape, in the 

 the drum and petrous portion of the temporal bone. Outwardly it is 

 its functions. bounded ^y the membrana tympani, and on other sides by 

 the petrous bone : it is crossed by a chain of bones, three in number, and 

 named the malleus or hammer-bone, the incus or anvil, and the stapes 

 or stirrup. The Eustachian tube affords a channel of communication 

 from the interior of the drum to the pharynx. Moreover, there is a com- 

 munication with the mastoid cells, but the Eustachian tube is the only 

 outlet to the atmosphere. The whole cavity of the tympanum is lined 

 with mucous membrane and ciliated epithelium, which is also reflected 

 over the bony chain. Upon the inner wall of the tympanum are two 

 chief apertures, the fenestra ovalis and the fenestra rotunda, each closed 

 by membrane. The chain of bones is attached at one end by the handle 

 of the malleus to the membrana tympani, at the other by the foot of the 

 stirrup to the membrane of the fenestra ovalis. 



