Mechanism of the Larynx. 331 



The law of vibration which I have above explained renders 

 this more intelligible; for since it appears that unless the mem- 

 branous edges of the passage are placed nearly parallel they can- 

 not be made to vibrate, we have only to suppose that the change 

 we feel in the Larynx is the placing of the ligaments in a parallel 

 position, and the whole mystery is explained. If therefore I can 

 succeed in shewing that the arrangement of the cartilages and 

 muscles is adapted for the purpose of placing the vocal ligaments 

 under the various conditions which have been shewn to be neces- 

 sary, I shall have done all that is possible to complete the 

 evidence in favour of my explanation. 



For, after all, no explanation of the functions of a machine, 

 of which essential parts are concealed while in action, can be com- 

 plete and uncontrovertible: when we have examined the separate 

 parts, and have enumerated the functions which observation shews 

 the machine to be capable of performing, and by comparing these 

 with the different portions here elicited, as we flatter ourselves, a 

 complete allotment of each function to its appropriate part of the 

 structure, we have only been in fact describing a machine of our 

 own contrivance, copied in form, and capable perhaps of per- 

 forming the same functions, but not necessarily identical with 

 the original, because we cannot certainly know whether it per- 

 forms the same motions for the same functions. Hence we can 

 only establish a probability that the uses of the corresponding 

 parts in the two are the same. Beyond this probability we can 

 never get, unless we can succeed in viewing the machine in 

 motion. 



This is not entirely the case with the Larynx, because we are 

 enabled to trace the motions of some of the cartilages from without ; 

 but the greater part of the machine is, and always must be, hidden 



Vol. IV. Part III. U u 



