MOVEMENTS OF THE GLOTTIS DURING PHONATION. 491 



Thyro-arytenoid Muscles. These 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 aryt- 

 enoid cartilages. Stimulation of the nervous filaments distributed to these 

 muscles renders the vocal chords tense. The great variations that may be 

 produced in the pitch and quality of the voice by the action of muscles oper- 

 ating directly or indirectly upon the vocal chords render the problem of de- 

 termining the precise mode of action of the intrinsic muscles of the larynx 

 complicated and difficult. It is certain, however, that in these muscular 

 acts, the thyro-arytenoids play an important part. Their contraction regu- 

 lates the thickness of the vocal chords, while at the same time it modifies 

 their tension. The swelling of the chords, which may be rendered regular 

 and progressive under the influence of the will, is one of the most important 

 elements in the formation of the timbre of the voice. 



Mechanism of the Production of the Voice. If the glottis be examined 

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

 chink during forced inspiration, due to the action of the posterior crico- 

 arytenoid muscles, can be observed without difficulty. This action is effected 

 by a separation of the posterior points of attachment of the vocal chords to 

 the arytenoid cartilages. During ordinary expiration, none of the intrinsic 

 muscles seem to act and the larynx is entirely passive, while the air is gently 

 forced out by the elasticity of the lungs and of the thoracic walls ; but so 

 soon as an effort is made to produce a vocal sound, the appearance of the 

 glottis undergoes a change, and it becomes modified in the most varied man- 

 ner with the different changes in pitch and intensity that the voice can be 

 made to assume. Although sounds may be produced, and even words may 

 be articulated, with the act of inspiration, true and normal phonation takes 

 place during expiration only. It is evident, also, that the inferior vocal 

 chords alone are concerned in this act. 



Movements of the Glottis during Phonation. It is somewhat difficult to 

 observe with the laryngoscope all of the vocal phenomena, on account of the 

 epiglottis, which hides a considerable portion of the vocal chords anteriorly, 

 especially during the production of certain notes ; but the patience and skill 

 of Manuel Garcia, a celebrated teacher of singing, enabled him to overcome 

 most of these difficulties, and to settle, by autolaryngoscopy, certain impor- 

 tant questions with regard to the action of the larynx in singing. It is for- 

 tunate that these observations were made by one versed theoretically and 

 practically in music and possessed of great control over the vocal organs. 



Garcia, after having observed the respiratory movements of the larynx, 

 as they have just been briefly described, noted that as soon as any vocal effort 

 was made, the arytenoid cartilages were approximated, so that the glottis 

 appeared as a narrow slit formed by two chords of equal length, firmly 

 attached posteriorly as well as anteriorly. The glottis thus undergoes a 

 marked change. A nearly passive organ, opening for the passage of air 



