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exception of a narrow slit; projecting beyond this extremity 

 of each of the tubes are two pieces of wood, so fashioned that 

 when this piece of elastic membrane is stretched across the 

 extremity of one tube, the surfaces of the membrane will 

 diverge slightly, while, if the same membrane be extended 

 across the other, the surfaces will be parallel, or a little con- 

 vergent. A column of air, as you may perceive, propelled 

 through the former tube, will only produce a rustling noise, 

 but in the case of the latter a distinct intonation will result. 



" It has been already stated that the manner in which this 

 adjustment of the vocal cords, so necessary for the production 

 of a sonorous vibration, is effected, has been a matter of contro- 

 versy and of doubt ; the most generally received opinion being 

 that it is accomplished by means of the thyro-arytenoid mus- 

 cles ; these latter are attached to the thyroid cartilage in front, 

 and to the arytenoid behind. Now, without analysing the 

 action of these muscles, in order to ascertain how far their 

 contractions could influence the parallel condition of the 

 cords, it may, however, be stated, that inasmuch as the mus- 

 cles and cords are attached to the same cartilages, the action 

 of the muscles will approximate the cartilages, and conse- 

 quently relax the vocal cords, a condition incompatible with 

 the production of high notes ; so that, even supposing these 

 muscles to be capable of eSecting the necessary adjustment 

 when a deep note is produced, they could not be used in the 

 production of a high intonation, a certain amount of tension 

 of the vocal cords being, under these circumstances, required. 

 The thyro-arytenoid is a most important muscle of the larynx ; 

 it can, in a marked degree, influence the condition of the vocal 

 cords, and is, no doubt, called into action every moment, in 

 regulating the varied and constantly changing tension of the 

 vocal cords ; but that it is capable of producing the required 

 parallel position of the cords cannot, we consider, be main- 

 tained; besides, it would constitute an anatomical eccentricity 

 that a motion so essential to the function of the larvnx that the 



