MECHANISM OF THE PRODUCTION OF THE VOICE. 553 



the articulations of the arytenoid cartilages with the cricoid will permit. In any event, 

 this muscle is important in phonation, as it serves to fix the posterior attachments of the 

 vocal chords and to increase the efficiency of certain of the other intrinsic muscles. 



Lateral Crico-arytenoid Muscles. These muscles are situated in the interior of the 

 larynx. They arise from the sides and superior borders of the cricoid cartilage, pass 

 upward and backward, and are attached to the base of the arytenoid cartilages. By 

 dividing all of the filaments of the recurrent laryngeal nerves, except those distributed to 

 these muscles, and then galvanizing the nerves, Longet has shown that they act to ap- 

 proximate the vocal chords, and to constrict the glottis, particularly in its interligamentous 

 portion. These muscles, with the arytenoid, act as constrictors of the larynx. 



Thyro-arytenoid Muscles. It is sufficiently easy to indicate the relations and attach- 

 ments of these muscles, but their mode of action is more complex and difficult of compre- 

 hension. When we come to study the conditions of the vocal chords involved in certain 

 modifications of the voice, we shall refer more in detail to the action of different fasciculi 

 of these muscles. In this connection, we shall only describe very briefly their situation 

 and attachments and the general results of their contraction. 



The thyro-arytenoid muscles are situated within the larynx. They are broad and flat, 

 and they arise in front from the upper part of the crico-thyroid membrane and the lower 

 half of the thyroid cartilage. From this line of origin, each muscle passes backward in two 

 fasciculi, both of which are attached to the anterior surface and the outer borders of the 

 arytenoid cartilages. The application of galvanism to the nervous filaments distributed to 

 these muscles has the effect of rendering the vocal chords rigid, increasing the inten- 

 sity of their vibrations. The great variations that may be produced in the pitch and 

 quality of the voice by the action of muscles operating directly or indirectly upon the vocal 

 chords render the problem of determining the precise mode of action of the intrinsic 

 muscles of the larynx exceedingly complicated and difficult. It is certain, however, that, 

 in these muscular acts, the thyro-arytenoids play an important part. Their contraction 

 regulates the thickness and rigidity of the vocal chords, while at the same time it modi- 

 fies their tension. The swelling of the chords, which may be rendered regular and pro- 

 gressive under the influence of the will, is one of the most important agents in the forma- 

 tion of the timbre of the voice. 



Mechanism of the Production of the Voice. 



It will save much unprofitable discussion to dismiss quite briefly most of the theories 

 that have been advanced to explain the production of the voice, and to avoid compari- 

 sons of the larynx with different kinds of musical instruments. Before the larynx had 

 been studied in action by means of the laryngoscope, physiologists, having the anatomical 

 structure of the parts for their only guide, presented various speculations with regard to 

 the mechanism of phonation, which were frequently entirely opposed to each other in 

 principle. The vocal apparatus was compared to wind or brass instruments, to reed- 

 instruments, to string-instruments, to the flute, etc., and some even refused to the vocal 

 chords any share in the sonorous vibrations. An apparatus was devised to imitate the 

 vocal organs, experiments were made with the larynx removed from the body, and every 

 thing seemed to be done, indeed, except to observe the organs in actual function. A short 

 time, however, after the laryngoscope came into use, the larynx was examined during the 

 production of vocal sounds. The true value of previous theories was then positively 

 demonstrated ; and, while it has not been possible to settle all disputed points with regard 

 to the precise mode of action of certain muscles, the appearances of the larynx itself dur- 

 ing phonation and the results of the action of certain of the intrinsic muscles have been 

 quite accurately described. 



Appearance of the Glottis during Ordinary Respiration. If the glottis be examined 

 with the laryngoscope during ordinary respiration, the wide opening of the chink during 



