ACTION OF ACCESSORY VOCAL ORGANS 443 



the crico-thyroid muscles are brought into action, and these are assisted 

 by the arytenoid and the lateral crico-arytenoids, which combine to fix 

 the posterior attachments of the vibrating ligaments. It will be 

 remembered that the crico-thyroids, by approximating the cricoid and 

 thyroid cartilages in front, increase the distance between the arytenoid 

 cartilages and the anterior attachment of the vocal chords. 



As the notes produced by the larynx become higher in pitch, the 

 posterior attachments of the chords are approximated, and at this time 

 the lateral crico-arytenoids probably are brought into vigorous action. 



The uses of the thyro-arytenoids are more complex; and it is 

 probably in great part by the action of these muscles that the varied 

 and delicate modifications in the rigidity of the vocal chords are 

 produced. 



The differences in singers as regards the purity of their notes and 

 intonation are due in part to the accuracy with which some put the 

 vocal chords on the stretch; while in those in whom the voice is of 

 inferior quality, the action of the muscles is more or less vacillating and 

 the tension frequently is incorrect. The fact that some singers can 

 make the voice heard above the combined sounds from a large chorus 

 and orchestra is not due entirely to the intensity of the sound, but in 

 great measure to the mathematical equality of the sonorous vibrations 

 and the comparative absence of discordant waves. 1 



Action of Accessory Vocal Organs. A correct use of the accessory 

 organs of the voice is of great importance in singing ; but the action of 

 these parts is simple and does not require an extended description. The 

 human vocal organs, indeed, consist of a vibrating instrument, the larynx, 

 and of certain tubes and cavities by which the sound is reenforced and 

 modified. 



The trachea serves, not only to conduct air to the larynx, but to 

 reenforce the sound to a certain extent by the vibrations of the column 

 of air in its interior. When a powerful vocal effort is made, it is easy 

 to feel, with the finger on the trachea, that the contained air is thrown 

 into vibration. 



The capacity of the cavity of the larynx is capable of certain varia- 

 tions. In fact, both the vertical and the bilateral diameters are dimin- 

 ished in high notes and are increased in low notes. The vertical 

 diameter may be modified slightly by ascent and descent of the true 

 vocal chords, and the lateral diameter may be reduced by the action of 

 the inferior constrictors of the pharynx on the sides of the thyroid 

 cartilage. 



1 The characters of musical sounds, both vocal and instrumental, will be considered in con- 

 nection with the physiology of audition. 



