PHYSIOLOGY. 



glottis, when expelled from the lungs. 

 Speech or articulated voice is produced 

 by this sound, modified by the motions ot 

 the tongue, lips, and other parts of the 

 mouth. It is obvious, therefore, that no 

 animals can have a voice, unless they 

 possess lungs. 



The larynx is the instrument of the 

 voice, of which the rima glottidis is the 

 immediate organ. Hence, it' the trachea 

 be opened below, so as to prevent the 

 air from passing through, the voice is 

 destroyed ; while, if the opening be made 

 above, the fpeech only is destroyed, 



It is universally agreed among physio- 

 logists, that the "air, expelled from" the 

 kings in expiration, striking against the 

 sides of the rima glottidis (chordae vo- 

 cales) constitutes the voice. But it is 

 necessary that the opening should be 

 placed in some condition produced by an 

 exertion of the will ; for although air is 

 constantly passing to and fro, the voice is 

 not formed unless by an express effort 

 for that purpose; neither is it formed 

 during sleep ; nor after the muscle!* of 

 the arytenoid cartilages have been para- 

 lysed by dividing their nerves. 



The manner in which the voice is 

 changed from acute to grave, and vice 

 versa, has been much disputed : whether 

 it arise from dilatation and contraction of 

 the aperture, or from tension and relaxa- 

 tion of the chordae vocales. On the lor- 

 mer supposition the human larnyx may 

 he compared to a wind instrument, in 

 which the enlargement of the aperture 

 renders the sound grave, and its diminu- 

 tion acute. By the latter explanation it 

 resembles a stringed instrument. After 

 considering the arguments on both sides, 

 \ve should be inclined to admit the ope- 

 ration of both causes. The change of the 

 voice from acute to grave at the time 

 of puberty, when the larynx undergoes a 

 remarkable developement, as well as its 

 acuteness in females, whose glottis is less 

 by one-third than that of man, shew that 

 the size of the aperture has a great in- 

 fluence Observing on the other hand 

 that the vocal chorus admit of considera- 

 ble tension and relaxation, we must allow 

 that these variations will render them 

 susceptible of executing, in^a given time, 

 vibrations more or less extensive and ra- 

 pid. And although they are neither dry, 

 stretched, nor isolated, which are neces- 

 sary conditions to the production of 

 sound in those stringed instruments to 

 which the larynx has been compared, 

 yet they are analogous to vibrating ob- 

 dies placed at the top of wind instru- 



ments, as the reed in hautboys, the 

 mouth-piece in flutes, &c. and equally 

 contribute to the formation and varied 

 inflexions of vocal sound. That all the 

 changes and conditions of the vocal or- 

 gans, of whatever description, necessary 

 to the production and modification of 

 sounds, are produced by the muscles of 

 the part, is rendered obvious by the ele- 

 gant experiment, in which the ligature 

 or section of one or both recurrent 

 nerves, or paria vaga, either signally im- 

 pairs, or entirely destroys, the vocal 

 powers of the animal. 



The modifications of the voice are also 

 affected by the length of the trachea ; 

 hence the larynx is manifestly drawn up 

 in the neck, in the tttterance of acute 

 sounds, and as plainly descends when a 

 grave sound is produced. In singing, 

 where these effects take place in a 

 greater degree, the head is thrown back 

 upon the neck in the former case, and 

 brought forwards on the chest in the lat- 

 ter. 



The voice is stronger in proportion to 

 the capacity of the thorax ; hence it is 

 weaker after meals, when the stomach, 

 distended by food, prevents the descent 

 of the diaphragm, and in consumptive 

 persons, where the capacity of the lungs 

 is diminished by disease. It acquires 

 more force and intensity, and becomes 

 more sonorous, by its reflections in the 

 mouth and nasal canals. Hence it is 

 disagreeably altered when its passage in 

 this direction is stopped by disease, as by 

 polypus, and it is then commonly, but 

 quite erroneously, said, that persons 

 speak through the nose. 



\Vhistling, which is common to man 

 with Dinging- birds, is produced in the lat- 

 ter by their double larynx ; but in the for- 

 mer it is effected by a contraction and 

 corrugation ot the lips, in imitation of the 

 effect produced by birds. 



In singing, the voice runs through the 

 different degrees of the harmonic scale 

 with more or less rapidity, changing from 

 acute to grave, and vice versa, with an 

 expression of the intermediate notes. It 

 requires much more exertion than speech. 

 The glottis enlarges and contracts, the 

 larynx is elevated or depressed, the neck 

 elongated or shortened, inspirations are 

 accelerated, prolonged or retarded ; ex- 

 pirations are long, or short and abrupt.. 

 The power of singing is peculiar to man, 

 and forms the great prerogative of his 

 vocal organs. Whistling is common al- 

 so to birds ; which are often taught to 

 pronounce words without any great diffi- 



