874 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



cords, together with superadded noises or modes of obstruction, con-sonants, 

 produced by action of the mouth-parts. The vowel sounds usually carry the 

 accent of syllables, and the consonants, for the most part, are sounded only 

 with, or represent peculiar modes of obstructing the former. No classification 

 of vocal signs can be made in which exceptions do not form important addenda 

 to general rules. 



Articulation is the modification of sound in speech, usually effected by action 

 of the lips, the tongue, the palate, or the jaws, and the place of articulation 

 depends, in any definite case, on the mode in which a sound is formed. Its use 

 as an expression of thought is the chief physiological distinction between man 

 and the lower animals. Distinctness of articulation, so essential to clearness 

 of language, not to mention its aesthetic value, depends on the accuracy of the 

 muscular adjustments used in forming sounds, especially consonantal sounds. 



The speaking is distinguished from the singing voice partly by the fact that 

 most sounds in the first case are articulate or formed in the mouth, while in 

 the latter their quality is only there modified. In singing the tone is sustained 

 at the same pitch for a considerable interval, while in speaking the voice is con 

 tinually sliding up and down on the vowel sounds. In speaking the conso- 

 nantal noises and obstructions are more prominent because of their more abrupt 

 formation. 1 - 2 



Vowel sounds owe their origin to vibration of the vocal cords, and their 

 quality to the selective resonance of the cavities above the cords. In sounding 

 the series of vowels, a, e, i, o, u (pronounced ah, a, e, o, oo), it is found that the 



U 



2* 



FIG. 304. Section of the parts concerned in phonation, and the changes in their relations in sound- 

 ing the vowels A (*), I ("), V () (after Landois and Stirling) : T, tongue ; p, soft palate ; e, epiglottis ; g, glot- 

 tis ; h, hyoid bone ; 1, thyroid ; 2, 3, cricoid ; 4, arytenoid cartilage. 



form and size of the mouth-cavity, the position of the tongue, the position of 

 the soft palate separating or allowing communication between the nasal and 

 pharyngeal cavities, undergo a progressive change (Fig. 304). Helmholtz has 

 shown that the vowel sounds owe their differences of quality to the varied 

 resonance of the mouth-cavity, dependent on its shape, through which now one, 

 now another, of the overtones in the note produced by vibration of the vocal 

 cords is reinforced. 3 This result is dependent on the fact that when the mouth 

 is set in position for the formation of the various vowel sounds the pitch of its 



1 Browne and Behnke : op. cit., p. 28. 



2 Monroe: Manual of Physical and Vocal Training, 1869, p. 51. 



3 Helmholtz : loc. cit. 



