628 TEXT-BOOK OF PHYSIOLOGY. 



the blending of a number of different vibrations. The quality of the sound 

 produced in the larynx is, however, modified by the resonance of the mouth 

 and nasal cavities; certain of the overtones being reinforced by changes in 

 the shape of the mouth cavity more especially, thus giving to the voice a 

 somewhat different quality. 



The Varieties of Voice. The region of the music scale, comprising 

 all vibrations between 32 and 2048 per second, with which laryngeal sounds 

 are hi accord will vary in the two sexes and in different individuals of the 

 same sex. It is customary to classify voices, especially those of singers, into 

 bass, baritone, tenor, contralto, mezzo-soprano, and soprano, in accordance 

 with the regions of the music scale with which they correspond. Thus the 

 succession of notes characteristic of the bass voice vary in pitch from F, fa p 

 to c', do 3 , or from 85 to 256 vibrations per second; those of the baritone 

 from A, la t , to f, fa 3 , of from 106 to 341 vibrations per second; those of the 

 tenor from c', do 2 , to a', Ia 3 , or from 128 to 427 vibrations per second; those 

 of the contralto from e, mi 2 , to c", do 4 , or from 160 to 512 vibrations per 

 second; those of the mezzo-soprano from g, so! 2 , to e", mi 4 , or from 192 to 

 640 vibrations per second; those of the soprano from b, si 2 , to g", so! 4 , or 

 from 240 to 768 vibrations per second. The range of the voice is thus seen 

 to embrace from one and three-quarters to two octaves. Some few individual 

 singers have far exceeded this range, but they are exceptional. 



Speech is the expression of ideas by means of articulate sounds. These 

 sounds may be divided into vowel and consonant sounds. 



The vowel sounds, a, e, i, o, u, are laryngeal tones modified by the 

 superposition and reinforcement of certain overtones developed in the mouth 

 and pharynx by changes in their shapes. The number of vibrations under- 

 lying the production of each vowel sound is a matter of dispute. 



Consonant sounds are produced by the more or less complete interruption 

 of the vowel sounds during their passage through the organs of speech. 

 These may be divided into : 



1. Labials, p, b, m. 



2. Labio-dentals, /, v. 



3. Linguo-dentals, s, z. 



4. Anterior linguo-palatals, /, d, /, n, r, sh, zh. 



5. Posterior linguo-palatals, k, g, h, y. 



The names of these different groups of consonants indicate the region of 

 the mouth in which they are produced and the means by which the air blast 

 is interrupted. 



THE NERVE MECHANISM OF THE LARYNX. 



The nerve mechanism by which the musculature of the larynx is excited 

 to action and coordinated so as to subserve both respiration and phonation 

 involves the fibers contained in the superior and inferior laryngeal nerves 

 (both branches of the vagus) and their related nerve-centers in the central 

 nerve system. 



For respiratory purposes it is essential that the lumen of the glottis shall 

 be sufficiently large to permit the entrance and exit of air without hindrance. 



