552 VOICE AND SPEECH 



two bands of animal membrane. Appliances of this kind, however, 

 do not give a correct picture of the action of the vocal cords, because 

 the vibratory parts of these models consist of closely approximated 

 bilipped membranes which oscillate toward one another. Never- 

 theless, they serve the useful purpose of demonstrating that the vocal 

 sounds, in agreement with the sounds produced by any musical in- 

 strument, differ from one another in loudness, pitch and quality. 



The loudness or intensity of a sound is determined by two factors, 

 namely, the volume and force of the expiratory blast of air and the 

 amplitude of the vibrations of the vocal bands in either direction from 

 their position of rest or equilibrium. These vibrations, moreover, are 

 greatly reinforced by the sympathetic oscillation of the walls of the 

 chest and head parts. 



The pitch of a sound depends upon the number of vibrations oc- 

 curring in a unit of time. Obviously, therefore, it is determined first 

 of all by the character of the vibrating body, i.e., by the length, 

 thickness and general elastic qualities of the vocal cords. Secondly, 

 it is dependent upon the degree of tension to which these bands are 

 subjected, the highest sounds being emitted when they are tightly 

 stretched beside a narrow glottis. As a rule, the outline of the latter 

 remains elliptical as long as the vibrations do not exceed 240 to the 

 second. Between 240 and 512 vibrations, on the other hand, the vocal 

 bands are gradually brought closer together until they eventually en- 

 velop merely the narrowest possible slit. In fact, the production of 

 very high notes requires an almost absolute approximation of these 

 bands so that only short segments of them are allowed to vibrate. At 

 this time, the vocal aperture or rima vocalis is restricted to a small oval 

 opening situated directly behind the anterior wall of the thyroid 

 cartilage. 



The foregoing very general reference to the structural peculiarities 

 of the vocal cords may serve as an explanation for the differences 

 in the pitch and quality of the voice in men and women. Since the 

 vocal bands of children are relatively short, the pitch of their voice 

 must be high. At puberty, however, the larynx develops very rapidly 

 in both sexes, a fact which readily accounts for the rather sudden 

 drop in the pitch of the voice occurring at this time. Moreover, 

 owing to the fact that the cords attain a greater length in men, this 

 "breaking" of the voice is especially pronounced in them. In most 

 instances, the voice of women acquires at this time merely a fuller 

 and richer character. If the development of distinct sex character- 

 istics is prevented by castration or by disturbances in the function 

 of the internal secretory organs, the larynx fails to undergo these 

 changes and the voice retains its peculiar high pitch and immature 

 quality. 



The quality of the sounds depends upon the character of the vibra- 

 tions. Like in any musical instrument, the vibrations of the vocal 

 cords are of the composite type, i.e., they are made up of fundamental 



