Chap, vii.] SPECIAL MUSCULAR MECHANISMS. 1091 



what we have insisted upon. Auditory sensations are at least 

 as important for the proper management of the voice as are 

 visual sensations for the movements of the eyes, and more im- 

 portant than are visual sensations for the movements of the body 

 and limbs. Indeed they are in a way essential to the very utter- 

 ance of the voice; the dumbness which is so conspicuous a con- 

 comitant of congenital deafness is in most cases due not to 

 deficiency in the muscular apparatus or even in the nervous 

 mechanism on what we may call its motor side, but to the lack 

 of afferent impulses from the auditory nerve. And in popular 

 language we recognize this dependence of the management of 

 the laryngeal muscles on auditory sensations when we talk of 

 such or such one, who is deficient in this respect, as " having no 



ear." 



§ 676. The ventricles of the larynx appear to be useful in 

 allowing the vocal cords sufficient room for their vibrations; 

 they also supply a secretion by which the vocal cords are kept 

 adequately moist. The purpose of the ventricular bands is not 

 exactly known ; it has been suggested that they may at times 

 exert a damping action by being brought down to touch the 

 vocal cords ; but this is very doubtful. The epiglottis, the 

 position of which as we have seen varies in different kinds of 

 voice, has also an influence on the character of the voice ; and 

 further influences which we shall consider under 'speech' are 

 exerted by the form of the pharynx and the mouth. 



§ 677. At the age of puberty a rapid development of the 

 larynx takes place, leading to a change in the range of the voice. 

 The peculiar harshness of the voice when it is thus ' breaking ' 

 seems to be due to a temporary congested and swollen condition 

 of the mucous membrane of the vocal cords accompanying the 

 active growth of the whole larynx. The change in the mucous 

 membrane may come on quite suddenly, the voice ' breaking ' 

 for instance in the course of a night. 



