loo THE POPULAR SCIENCE MONTHLY. 



case of the muscles moving the chest and the vocal cords naturally- 

 produced sound that is to say, voice. These movements, at first 

 accidental and purposeless, in time became inseparably associated 

 with the emotional state giving rise to them, so as to coincide with 

 it, and thus serve as an index or expression thereof. From this 

 to the voluntary emission of vocal sounds is an easy step, and it 

 is probable enough that the character of those sounds was prima- 

 rily due to the " imitation and modification of different natural 

 sounds, the voices of other animals, and man's own instinctive 

 cries. 



The mechanism of the voice is extremely simple in its general 

 principles, though highly complex in its details. Fortunately, a 

 knowledge of the latter is not required for the comprehension of 

 the main facts relative to the production of the voice, and I shall 

 not further allude to them here. Vocal sound is produced solely 

 in the larynx, an elementary fact which must be thoroughly 

 grasped, as many absurd notions are current even among people 

 who should know better, such as that the voice may be produced 

 at the back of the nose, in the stomach, and elsewhere. The 

 larynx is a musical instrument of very complex structure, partak- 

 ing both of the reed and the string type, the former, however, dis- 

 tinctly predominating. It is essentially a small chamber with 

 cartilaginous walls, which is divided into an upper and a lower 

 compartment by a sort of sliding floor, or double valve, formed by 

 the two vocal cords. In breathing this valve opens, its two lateral 

 halves gliding wide apart from each other, so as to allow a broad 

 column of air to pass through ; in speaking or singing, on the 

 other hand, the valve is closed, but for a narrow rift along its 

 middle. Through this small chink the air escaping from the lungs 

 is forced out gradually in a thin stream, which is compressed, so 

 to speak, between the edges of the cords, that form the opening 

 technically called the "glottis," through which it passes. The 

 arrangement is typical of the economical workmanship of Nature. 

 The widest possible entrance is prepared for the air which is taken 

 into the lungs, as the freest ventilation of their whole mucous 

 surface is necessary. When the air has been fully utilized for 

 that purpose, it is, if need be, put to a new use on its way out for 

 the production of voice, and in that case it is carefully husbanded 

 and allowed to escape in severely regulated measure, every parti- 

 cle of it being made to render its exact equivalent in force to work 

 the vocal mill-wheel. When the air is driven from the lungs up 

 the windpipe it strikes against the under surface of the floor or 

 double valve formed by the vocal cords, which are firmly stretched 

 to receive the shock, forces them apart to a greater or less extent, 

 and, in rushing out between them, throws them into vibration. 

 * " Descent of Man," second edition, 1882, p. 87. 



