550 HANDBOOK OF PHYSIOLOGY. 



find two series of sounds: in one the sounds are mute, and cannot be 

 uttered with a vocal tone; the sounds of the other series can be formed 

 independently of voice, but are also capable of being uttered in con- 

 junction with it. 



All the vowels can be expressed in a whisper without vocal tone, that 

 is, mutely. These mute vowel-sounds differ, however, in some meas- 

 ure, as to their mode of production, from the consonants. All the 

 mute consonants are formed in the vocal tube above the glottis, or in 

 the cavity of the mouth or nose, by the mere rushing of the air between 

 the surfaces differently modified in disposition. But the sound of the 

 vowels, even when mute, has its source in the glottis, though its vocal 

 cords are not thrown into the vibrations necessary for the production of 

 voice; and the sound seems to be produced by the passage of the current 

 of air between the relaxed vocal cords. The same vowel-sound can be pro- 

 duced in the larynx when the mouth is closed, the nostrils being open, 

 and the utterance of all vocal tone avoided. The sound, when the mouth 

 is open, is so modified by varied forms of the oral cavity, as to assume 

 the characters of the vowels a, e, i, O, u, in all their modifications. 



The cavity of the mouth assumes the same form for the articulation 

 of each of the mute vowels as for the corresponding vowel when vocal- 

 ized; the only difference in the two cases lies in the kind of sound 

 emitted by the larynx. It has been pointed out that the conditions 

 necessary for changing one and the same sound into the different vowels, 

 tire differences in the size of two parts the oral canal and the oral open- 

 ing; and the same is the case with regard to the mute vowels. By oral 

 canal, is meant here the space between the tongue and palate: for the 

 pronunciation of certain vowels both the opening of the mouth and the 

 space just mentioned are widened; for the pronunciation of other vowels 

 both are contracted; and for others one is wide, the other contracted. 

 Admitting five degrees of size, both of the opening of the mouth and of 

 the space between the tongue and palate, Kempelen thus states the 

 dimensions of these parts for the following vowel-sounds: 



Vowel. Sound. Size of oral opening 1 . Size of oral canal, 



a as in "far" 5 3 



a bi name" 4 



e " "theme" 3 



o " "go" 2 



oo " "cool" 1 



Another important distinction in articulate sounds is, that the utter- 

 ance of some is only of momentary duration, taking place during a sud- 

 den change in the conformation of the mouth, and being incapable of 

 prolongation by a continued expiration. To this class belong b, p, d, 

 and the hard g. In the utterance of other consonants the sounds may 

 be continuous; they may be prolonged, ad libitum, as long as a particu- 

 lar disposition of the mouth and a constant expiration are maintained. 



