600 ARRANGEMENT OF THE LARYNX. 



of the elasticity of the elastic plates. In the case of membranous reeds, and also 

 in that of silk, it is directly proportional to the square root of the extending weight, 

 which in the larynx corresponds to the force of the tensor muscles. 



(c) In the case of membranous reeds a more powerful blast not only strengthens 

 the tone by increasing the amplitude of vibration, but it also raises the pitch of 

 the tone, because the greater amplitude of vibration increases the mean tension 

 of the elastic membrane. 



Among physical influences the following further are to be noted: 



(d) The reinforcing tube, which is exceedingly variable in form, also resounds 

 when the larynx is intonated ; its primary tone is mingled with the sound of the 

 elastic reeds, and, thus, it is able to reinforce certain overtones of the latter. 

 This subject will be discussed in greater detail in the section on voice-formation. 

 The individual characteristics of the voice depend essentially upon the form of 

 the reinforcing tube. In reed-instruments the pitch of the tones can undoubtedly 

 be influenced by varying lengths of the reinforcing tube; but this is not taken 

 into consideration in the case of the larynx. 



(e) During intonation of the reeds the strongest resonance takes place in the 

 air- tube, as the latter contains compressed air. This causes the vocal resonance 

 that is heard when the ear is applied to the chest-wall. Strong intonation may 

 even cause an accompanying vibration of the thoracic wall. In weak individuals, 

 and in cases of falsetto voice, the vocal resonance is exceedingly slight. 



(/) Narrowing or widening of the glottis has no effect on the pitch of the 

 tone; but with the glottis wide open, disproportionately more air must pass 

 through it, thus materially increasing the work of the thorax. 



ARRANGEMENT OF THE LARYNX. 



Cartilages and Ligaments of the Larynx. The fundamental framework of the 

 larynx is formed by the cricoid cartilage, which is shaped like a seal-ring. The 

 inferior cornu of the thyroid cartilage articulates with the cricoid in its postero- 

 lateral region. This joint allows the plate of the thyroid cartilage to tilt forward, 

 the inclination occurring as a rotatory movement about a horizontal axis connecting 

 the two joints, the upper border of the cartilage moving forward and downward. 

 The joints also permit a slight shifting of the thyroid cartilage on the cricoid 

 upward and downward, forward and backward. The triangular, pyramidal 

 arytenoid cartilages articulate on the upper border of the plate of the cricoid 

 cartilage to one side of the median line, forming approximately a saddle-shaped 

 joint with oval articular surfaces. The latter permit a double movement on the 

 part of the arytenoids, namely rotation on their base about their vertical, some- 

 what oblique, longitudinal axis, by which the vocal process directed forward is 

 rotated outward and upward, and the muscular process directed outward and 

 overlapping the border of the cricoid cartilage posteriorly is rotated inward and 

 downward, or conversely. In addition, the arytenoid cartilages may be displaced 

 somewhat inward or outward on their bases. 



The true vocal bands, or vocal ligaments, are composed principally of elastic 

 fibers. They arise close together from about the middle of the internal angle of 

 the thyroid cartilage, and are inserted on the vocal processes of the arytenoid 

 cartilages directed forward. The "ventricles of Morgagni" allow free play for 

 the vibrations of the bands, and separate them from the upper "false" bands, 

 or ventricular ligaments, which are covered by a fold of mucous membrane. The 

 latter take no part in phonation. Numerous mucous glands of the mucous mem- 

 brane keep the vocal bands moist. 



In accordance with the functions of the laryngeal cartilages in connection 

 with the voice-apparatus, C. Ludwig has called the cricoid the "foundation-carti- 

 lage," the thyroid the "tension-cartilage," and the arytenoids the "position- 

 cartilages." 



Owing to the oblique downward inclination of their under surfaces the vocal 

 bands readily come together when the glottis is narrowed during inspiration (for 

 example in sobbing) ; and if the glottis is already closed, inspiration makes this 

 closure still firmer. The false vocal bands exhibit the opposite relation, for when 

 in mutual contact they are readily separated during inspiration; while during 

 expiration they readily close, owing to the inflation of the ventricles of Morgagni. 



Action of the Laryngeal Muscles. Dilatation of the glottis is effected 

 by the posterior crico-arytenoid muscles. In drawing the muscular 



