The whole of the inner surface of the larynx is lined with mucous membrane, though that covering over the true vocal bands is very thin, and so does not cause them to appear red like the false vocal bands, which are merely folds of the mucous membrane. However, the true vocal bands may become red and thickened when inflamed, because of this same mucous membrane, which, though ordinarily not visible to the eye, becomes so when the condition referred to is present; for inflammation is always attended by excess in the blood supply, with a prominence of the small blood-vessels resulting in a corresponding redness. The same thing happens, in fact, as in inflammation of the eyes or the nose, both of which are more open to observation. Bearing this in mind one can readily understand why in such a condition, which is often approached if not actually present in the case of "a cold," the voice becomes so changed. Such vocal bands are clumsy in movement, as the arms or any other part would be if thus swollen. The plain remedy is rest, cessation of function—no speaking, much less attempts at singing. Like the nose the larynx, and especially the vocal bands, may be catarrhal, and such a condition may call for medical treatment before the speaker or singer can do the most effective vocal work.
While the false vocal bands have little or nothing to do with phonation directly, they do serve a good purpose as protectors to the more exalted true vocal bands. When coughing, swallowing, vomiting, holding the breath tightly, etc., these folds of mucous membrane close over the true bands, often completely, and thus shut up for the moment the whole of that space between the bands known as the glottis, or glottic chink, to which reference was made in a previous chapter as the space through which the air finally gains access to the lungs.
Fig. 25 (Spalteholz). A view of the larynx from behind. Several of the muscles are well shown, of which the two indicated above are of the most importance. The arytenoideus proprius tends to bring the cartilages from which it is named, and therefore the vocal bands, toward each other; while the posterior crico-thyroid, from its attachments and line of pull, tends to separate these and lengthen the vocal bands.
Fig. 26 (Spalteholz). Showing structures as indicated above. The mucous membrane, that naturally covers all parts within the vocal mechanism, has been dissected away to show the muscles.
Fig. 27 (Spalteholz). Showing the parts indicated above; and of these the crico-thyroid muscle is to be especially observed. The oblique (especially so in the posterior part) direction of its fibres is evident, so that when it contracts, it must pull up the ring cartilage in front, and so tilt back its hinder portion and with it the arytenoid cartilages, and so lengthen and tense the vocal bands, as in the utterance of low tones.
The true vocal cords (which, because of having some breadth and being rather flat, are better termed vocal bands) are composed largely of elastic tissue. The reader may be familiar with this structure, which is often to be found in the portions of the neck of the ox that the butcher sells as soup beef. It is yellow in color, and stretching it has furnished many a boy with amusement. It is so unmanageable when raw that when it falls to the dog he usually bolts it, the case being otherwise hopeless. Such elastic tissue is, however, the very material for the construction of vocal bands, as they require to be firm yet elastic.
