crico-arytenoids in pulling the two arytenoid cartilages together, thus aiding in closing the glottis.

2. Extrinsic Muscles. In addition to the intrinsic muscles of the larynx, there are two rather important extrinsic muscles. These are the sterno-thyroid and the thyro-hyoid.

a. The sterno-thyroid. The sterno-thyroid, as its name implies, is attached to the thyroid cartilage and to the sternum or breast bone. Its action is to pull the whole larynx downward. When this muscle contracts it exerts a pressure upon the thyroid gland, through which comes the blood supply of the larynx. The action of the sterno-thyroid muscle as it depresses the whole larynx may be a factor in causing a depression of the epiglottis. This action probably has a muffling effect upon the deep low tones and may be in some measure responsible for the guttural and pectoral qualities which we shall discuss in the chapter on vocal quality.

b. The thyro-hyoid. The hyoid bone (Fig. 10) is held in place by various muscles attached to portions of the skull. This hyoid bone is suspended by muscular connections with the skull, and largely through the agency of this thyro-hyoid muscle, the larynx is suspended from the hyoid bone. When this muscle contracts, the larynx is pulled upward. It is easy to observe this action in swallowing.

We have, then, in the intrinsic and extrinsic musculature of the larynx, a relatively simple mechanism which is capable of a practically infinite number of adjustments. The cricothyroid muscle pulls the front portion of the cricoid cartilage and the front portion of the thyroid cartilage together, thus tipping back the arytenoid cartilages to which the posterior ends of the vocal folds are attached. This is probably the principal mechanism for tensing the vocal folds. The action of the other intrinsic muscles, as has been shown, is to move the vocal folds together and to draw them apart again, thus opening and closing the glottis. The vocal folds are themselves the edges of muscles and in a sense act to relax them

4 This is really a pair of muscles, one on each side of the thyroid cartilage.

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selves. Probably the most important function of the extrinsic muscles which move the larynx as a whole upward and downward is to change the position of the vocal folds with reference to the pharynx, thus controlling pharyngeal resonance.

III. THE RESONATORS

We have now examined the vibrator of the vocal apparatus, the larynx, in considerable detail. If there were no further mechanism to be explained, we should be at a loss to account for the intensity and even the audibility of vocal tones. The tones initiated by the vibrator have to be built up and reinforced by what are known as resonators. If a violin string be stretched to its usual degree of tension between two wooden posts and then bowed as in playing the instrument, nothing more than a weak, colorless tone is produced. When, however, the same string is stretched over the bridge of the violin and caused to vibrate, the body of the instrument (acting as a resonator) reinforces the fundamental tone and the overtones which are produced by the vibration of the string as a whole and its simultaneous vibration in parts, and we get the rich powerful tone of the violin. You will observe that all musical instruments have resonators. The piano has its sounding board, and the organ its pipes. The brass wind instruments, which are probably more like the human vocal mechanism than any other instruments, are nothing more than resonators, the human lips themselves furnishing the vibrations which are resonated by the metal tubes of the instruments. The difference between the vibration which you hear when you place your lips close together and expel air through them and the sounds which issue from the cornet, for example, is essentially a matter of what we call resonance.

The Western Electric Company has placed on the market an artificial larynx which makes it possible for a person to use his voice when for some cause he has had his larynx removed. In some cases of cancer of the throat, for example, it

is necessary to remove the larynx. The usual surgical procedure in such operations is to bring the upper end of the

trachea out through an opening in the front of the neck just above the collar bone. The artificial larynx is a very simple device which consists of a rubber tube the opening to which is

secured in an air-tight fashion over the opening of the trachea, a small hard rubber box across the interior of which a rubber band is stretched, and a hard rubber tube from the top of this box to convey the vibrations produced by the rubber band into the mouth of the person using the device. When one blows into this instrument, causing the rubber band to vibrate, nothing more than a monotonous humming sound is heard. When this sound is introduced into the mouth, however, it is resonated in such fashion that a relatively close approximation to normal voice is produced, the main difference between the sounds thus produced and those of the normal voice being in the lack of pitch variation in the fundamental tone. This invention is explained here merely to show the function of resonance in voice production.

Every vocal tone is a composite of vibrations. As we have said, the vocal folds vibrate over their whole length and probably as in the case of other vibrating bodies, they vibrate in segments. The longer the vibrator, the slower its vibrations; the shorter the vibrator, the more rapid its vibrations. These more rapid vibrations produced by the tendency of the vibrator to break up into segments are what we call upper partials or overtones. These tend to maintain a definite mathematical ratio with the lower tone which is called the fundamental and fuse with it in such a way as to produce a rich, full, musical tone. We shall explain this mechanism in greater detail in the following chapter on Vocal Quality. The important thing for us here is to note the fact that resonance is a matter of extreme importance in vocalization, and then to examine the principal resonators which are available for use in voice production.

A. The Pharynx. In Section I of this chapter we have described the pharynx. The pharynx is undoubtedly one of the principal resonators of the human voice. It is a relatively large bag-like structure the side and rear walls of which are wholly muscular and lined with mucous membrane. The elaborate set of muscles which compose the walls of the pharynx

can operate to produce almost any conceivable modification in its vertical or horizontal diameter. It can be left wide open at the top and drawn to a point at the bottom, forming a funnel-shaped cavity; it can be left wide open at the bottom and constricted at the top. In short, it is so modifiable in shape that it has great possibilities as a resonator. The most important changes in shape are doubtless those in length. If a glass tube be placed in a jar of water and a tuning fork held over the open end of the tube, it will be found that by moving the tube up and down we can locate a point at which the length of the portion of the tube out of the water, and therefore capable of acting as a resonator, is just right to give maximum reinforcement to the vibrations of the tuning fork. A surprising increase in the volume of the tone at this point not only shows clearly the function of the resonator, but it demonstrates that for each pitch there is a cavity of given size which gives maximum reinforcement to the tone. Therefore, as the length of the pharynx is increased and decreased, it can be fitted with great precision to resonate the different vocal tones produced in the larynx.

B. The Mouth. Here, again, we have the necessary mechanical apparatus for a resonator of variable size. The mouth has at least one advantage over the pharynx as a resonator in that it has several extremely hard bony surfaces which are important in a resonator. The hard palate, usually called the roof of the mouth, viewed from below is a concave or arched surface terminating at its lower edges in the gums and the teeth. The shape of the mouth as a resonator is of course controlled in the first instance by the movements of the lower jaw; second, by the almost unlimited possibility of movement in the tongue; third, by the activity of the velum or soft palate which forms the posterior portion of the palate; and, finally, by the movements of the lips. The control of the tongue, the soft palate, lips, and lower jaw is a matter of prime importance in speech, not only for purposes of articulation but also for resonance.