It is situated below the thyroid cartilage, with which it is connected by a membrane, the crico-thyroid. The wider part of this signet-ring is situated behind, where it affords attachment to large muscles. It also furnishes a base of support for two very important structures, the _arytenoid_ (_arutaina_, a ladle) cartilages. As the vocal bands are attached behind to them, and as they have a large degree of mobility, they are from a physiological point of view the most important of all the solid structures of the larynx.
There are two pairs of small bodies, the _cartilages of Santorini_, or _cornicula laryngis_, surmounting the arytenoids, and the _cuneiform_, or _cartilages of Wrisberg_, situated in the folds of mucous membrane on each side of the arytenoids; but these structures are of little importance.
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 s.p.a.ce between the bands known as the glottis, or glottic c.h.i.n.k, to which reference was made in a previous chapter as the s.p.a.ce through which the air finally gains access to the lungs.
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 amus.e.m.e.nt. 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.
[Ill.u.s.tration: 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.]
[Ill.u.s.tration: 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.]
[Ill.u.s.tration: 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.]
[Ill.u.s.tration: FIG. 28 (Spalteholz). A back (posterior) view of the larynx, etc. Note how the arytenoid cartilages rest on the cricoid; how the epiglottis overhangs, as its name implies, the glottis; and that the posterior part of the windpipe is closed in by soft structures, including (unstriped) muscle.]
It is important to remember the relative position of parts and to bear in mind that most of the laryngeal structures are in pairs. To this last statement the thyroid and cricoid cartilages and the epiglottis are exceptions, being single.
Of the _epiglottis_, a flexible cartilage, it is necessary to say little, as its function in voice-production, if it have any, has never been determined. It hangs as a flexible protective lid over the glottis, and food in being swallowed pa.s.ses over and about it. It no doubt acts to keep food and drink out of the larynx, yet in its absence, in some cases, owing to disease, no very great difficulty was experienced, probably because certain muscles acted more vigorously than usual and tended to close up the glottic c.h.i.n.k.
The following simple diagram will, it is hoped, make the relative position of parts plain so far as the anterior (front) attachments of parts to the thyroid cartilage are concerned. It will be understood that the inner anterior surface is meant, and that by "middle line"
is intended the middle line of the body, the imaginary vertical diameter pa.s.sing like a plumb-line from the middle plane of the head, let us suppose, downward just in front of the larynx.
[Ill.u.s.tration: FIG. 29.]
The angle made above and in front where the two wings of the thyroid cartilage meet is termed _Adam"s apple_ (_Pomum Adami_), and in some cases, mostly males, is very prominent. Adam"s apple has in itself, however, no special significance in voice-production.
The little concavity between the false vocal bands above and the true vocal bands below is termed the _ventricle of the larynx_. It allows of more s.p.a.ce for the free movements of the bands, especially those more important in voice-production.
The vocal bands are attached behind to the projecting angle of the base of the arytenoid cartilage, which is itself somewhat triangular in shape, the base of the triangle being downward and resting on the upper and posterior (back) surface of the cricoid cartilage, with which it makes a free joint, so that it can move swivel-like in all directions. This is most important, because through it is explained the fact that the vocal bands may be either tensed and lengthened or relaxed and shortened.
_The muscles act on these movable cartilages, and nearly all the changes in the vocal bands are brought about through the alterations in position of the arytenoid cartilages, to which they are attached behind._
Before describing the muscles of the larynx, the reader is reminded of the order of structures from above downward, in front, which is as follows:
The hyoid bone.
The thyro-hyoid membrane.
The thyroid cartilage.
The crico-thyroid membrane.
The cricoid cartilage.
The trachea.
The latter is connected with the cricoid cartilage by its membrane.
All the above structures can be felt in one"s own person, the more readily if he be thin and have a long neck. The hyoid bone, or tongue-bone, is that hard structure just above the cricoid cartilage, and which one may easily demonstrate to be much more movable than the larynx itself. The tongue muscles are attached to it above, and from it, below, the larynx is suspended, as already explained.
The muscles of the larynx are best understood if the principle of antagonistic action already referred to be remembered. Speaking generally, the muscles are arranged _in pairs_ which have an opposite or antagonistic action--viz.: (1) Those that open and close the glottis; (2) those that regulate the tension, or degree of tightness, of the vocal bands.
1. The muscles whose action tends to approximate the vocal bands--the _adductors_--are the _arytenoid[=e]us proprius_ and the _thyro-arytenoid[=e]us_. The former is attached to the posterior or back surface of both arytenoid cartilages; the latter, as its name indicates, to the anterior and inner surface of the thyroid and the anterior lower surface or angle (_vocal process_) of the arytenoid.
The opening or widening of the glottis is effected on each side (one muscle of the pair and its action being alone described in this and other cases) by the antagonist of these muscles, the _crico-arytenoid[=e]us posticus_, whose attachments are exactly as indicated by the names--viz., to the posterior part of the two cartilages named. When reading the description of these or other muscles it is absolutely necessary to have a pictorial ill.u.s.tration or the real object before one. The pull of this muscle is from the more fixed point, as in all other cases; hence the force is applied in a direction from below and outward, with the result that the arytenoid cartilage is tilted outward, and with it the vocal band is moved from the middle line.
[Ill.u.s.tration: FIG. 30 (Chapman). Diagram showing action of crico-thyroid muscle, stretching of the vocal cords, and lengthening of them. The dotted lines indicate the position a.s.sumed when the muscle has contracted.]
[Ill.u.s.tration: FIG. 31 (Spalteholz). View of the larynx as looked at from above. The ill.u.s.tration shows particularly well both the true and the false vocal bands. The true vocal bands are placed much as they are when a barytone is singing a very low tone. The part of the figure lowest on the page represents the back part of the larynx.]
[Ill.u.s.tration: FIG. 32 (Spalteholz). A cross-section transverse to the larynx, such as can be readily made with a strong knife.]
The _crico-thyroid_ also tends to open the glottis. Just as the diaphragm is the most important muscle of breathing, so is the crico-thyroid the most important in ordinary speaking and in singing in the lower register. It is a relatively large and strong muscle with an oblique direction in the main, though it is composed in reality of several sets of fibres some of which are much more oblique in direction than others (Fig. 28). As its name indicates, its points of attachment are to the thyroid and the cricoid cartilages, but the most fixed point (_origin_) is its point of attachment to the larger cartilage; hence its direction of pull is from the thyroid, with the result that the anterior part of the cricoid is drawn up, the posterior part down, and the arytenoid cartilage, resting on the upper part of the cricoid, backward, so that the vocal band is rendered longer and more tense (see especially Fig. 29). It is important to note that this is the muscle most used in singing the lower tones of the scale, and that its action must necessarily cease, to a great extent, when a certain point in the pitch is reached, as there is a limit to the degree of contraction of all muscles; and, besides, the crico-thyroid s.p.a.ce is of very moderate size, and the cricoid cartilage can ascend only within the limits thus determined. It thus follows that Nature has provided in the change of mechanism for a new register, which is nothing else than a change of mechanism with a corresponding change of function. It will be at once apparent that the claim that registers are an invention of men, and without foundation in nature, is without support in anatomy and physiology. The crico-thyroid is probably, however, of much more importance to tragic actors and barytones than to tenors or sopranos. This, however, is no excuse for the neglect of its development by the latter cla.s.s, as often happens, for without it the best tones of the lower register are impossible. On the other hand, the elocutionists who prescribe for students practices that involve the excessive use of this muscle, with a cramped position of the vocal organs, the larynx being greatly drawn down, with the view of producing disproportionately heavy lower tones, must take no comfort from the above anatomical and physiological facts. Art implies proportion, and it was one of the ambitions of all the best actors in the golden age of histrionic art to have an "even voice"--_i.e._, one equally good through the whole range required. The tragic actor, elocutionist, and public speaker, and the singer, whether soprano or ba.s.s, should neglect no muscle, though they may be justified in developing some in excess of others, but ever with a watchful eye on the weakest part.
2. The muscles which regulate the tension of the vocal bands are the following:
(_a_) The _thyro-arytenoid[=e]us_ (pair), which by tilting the arytenoid cartilages forward relaxes the tension of the vocal bands.
When they act with the adductors--_e.g._, the arytenoid[=e]us proprius--the result must be relaxation and approximation behind, which implies a greater or less degree of shortening, as usually happens when a certain point in an ascending scale is reached in persons whose methods of voice-production have not been in some way modified, and a new register begins, which in most female voices is marked by a more or less distinct and abrupt alteration of the quality of the tone.
The crico-thyroids are the antagonists of the above-named muscles, and they may act either very much alone or, to some extent, in cooperation with the above, to regulate or steady their action; for in movements so complicated as those required for voice-production it is highly probable that we are inclined to reduce our explanations of muscular action to a simplicity that is excessive, and to appreciate but inadequately the delicacy and complexity of the mechanism and the processes involved. It is quite certain that in the production of the highest tones of a tenor or soprano several muscles cooperate, and one, especially, seems to be of great importance in the formation of such tones, most of all, perhaps, in high sopranos. The muscle referred to is the thyro-arytenoid already described. It is not only attached to the two cartilages indicated by its name, but also along the whole of the external or outer surface of the vocal band. It will be remembered that practically all the muscles are arranged in pairs, one on each side of the middle line. The muscle now under consideration, more, perhaps, than any other, is complex in its action. Apparently a very few of its fibres may act more or less independently of all the others at a particular moment and with a specific and very delicate result, a very slight change in pitch.
Exactly how this is attained no one has as yet adequately explained; but it is doubtful whether any singer who does not possess a perfect control over this muscle can produce the highest tones of the soprano with ease and effectiveness. It is especially the muscle of the human birds of the higher flights.
(_b_) To these thyro-arytenoids, which for most singers and all speakers are probably chiefly relaxing in action, must be added as aiding in this function another pair, the _lateral crico-arytenoids_.
They are situated between the cricoid and arytenoid cartilages, and the direction of action is obliquely from below and forward, upward, and backward, so that the arytenoids are brought forward and also approximated more or less, which involves relaxed tension, at least, possibly also shortening of the vocal bands.
When a tenor or soprano singer reaches the upper tones, say about [Ill.u.s.tration: e" f" g"], or higher, there is considerable closing up in the larynx, much in the way in which the parts of the month are brought together in sucking. This is termed _sphincter action_, the mouth and the eyes being closed by such action, of which they are the most easily observed examples. As a result of this squeezing there is in some cases that reddening of the face and that tightness which is often felt uncomfortably, and which is _straining_, because when present in more than a very slight degree it is injurious, owing to congestion or acc.u.mulation of blood in the blood-vessels, with all the bad consequences of such a state of things. When the tightening does not go beyond a certain point it is normal--indeed, such sphincter action is inevitable; but it is the excess which is so common in tenors and others who strain for undue power, and to produce tones too high in pitch for their development or their method, which is so disastrous to the throat and to the best art also.
[Ill.u.s.tration: FIG. 33 (Spalteholz). Shows various structures, and especially well the false and the true vocal bands, with the s.p.a.ce between them (ventricle of Morgagni), but which has no special function in phonation, unless it acts as a small resonance-chamber, which is possible. This s.p.a.ce is a natural result of the existence of two pairs of vocal bands in such close proximity.]
[Ill.u.s.tration: FIG. 34 (Spalteholz). Parts have been cut away to expose to view the whole of the inner surface of the larynx (lined with mucous membrane). An excellent view of the vocal bands and of the "ventricle" of the larynx, between them, is afforded.]
When the vocal bands are in action their vibrations are accompanied by corresponding vibrations of the cartilages of the larynx--a fact of which any one may convince himself by laying his fingers on the upper part of the thyroid, especially when a low and powerful tone is produced. This vibration is not confined to the larynx, but extends to other parts--_e.g._, the chest itself, for when one speaks or sings a distinct vibration of the chest walls can be felt, though the extent to which this is present is very variable in different persons. As an ascending scale is sung the larynx can be felt (by the fingers) to rise, and the reverse as the pitch is lowered. This is due partly to the action of those muscles attached to the larynx which are not connected with the movements of the vocal bands, and partly to the influence of the expiratory air-blast. The glottis, partially closed as it must be in phonation, presents considerable resistance to the outgoing stream of air, hence the upward movement of the larynx when it is left free, and not held down by muscular action.
In singing and speaking the larynx should be steadied, otherwise the "attack," or application of the air-blast to the vocal bands, cannot be perfect. On the other hand, it is obviously incorrect to attempt to hold the larynx always in the same position. Holding down this organ by main force, as in the production of the so-called "straw ba.s.s," is one of the surest methods of producing congestion and consequent disorders of the vocal organs; and the author wishes to warn all voice-producers against such unnatural practices. Students of elocution and young actors often sin in a similar way, and "clergyman"s sore throat" is almost always due to this or some similar misuse of the vocal organs. One"s own sensations and common sense should never be disregarded, however eminent the teacher who recommends unphysiological methods.
PRACTICAL CONSIDERATIONS.
When the student has read the above description of the structure and functions of the larynx, and studied the ill.u.s.trations well, he will be prepared to deal with the subject in a practical manner, and without that it is feared his ideas will remain somewhat hazy.
First of all, he should try to find the parts mentioned in his own person, following this up by examinations of others, for which purpose children make good subjects, as they have usually necks that are not too deeply padded with fat, and they may be easily led to take the examinations as a sort of fun.
From above downward one feels in the middle line the parts in the order previously mentioned, beginning with the hyoid bone. One may learn that the larynx is movable and yielding, a hard structure covered with softer tissues, but what these are, and much more, can only be learned by examination of the larynx after it has been removed from some animal. Every butcher can provide the material for getting a sound, practical knowledge of the respiratory apparatus. He may be asked to supply the following:
1. A pig"s "pluck"--_i.e._, the "lights," or lungs, with the windpipe attached. The liver, heart, etc., are not required, though to observe the relations of the circulatory system--_i.e._, the heart and large blood-vessels--to the respiratory system will be time well spent.
Unless special instructions are given, the larynx, which the butcher may term the "weezend," may be lacking or mutilated. It should be explained that this organ, with a part of the windpipe and the extreme back part of the tongue, and all below it, are required. For one sitting this single "pluck" will suffice, as it will serve for a general examination. The lungs may be dilated by inserting a tube into the windpipe, tying it in position, and blowing into it with greater or less force. It should be especially observed how suddenly the lungs collapse when the breath force is removed, as this ill.u.s.trates well their _elasticity_. By cutting through the windpipe lengthwise and following it downward one learns how numerous are the branches of the bronchial tree, etc.
For a second sitting one should secure at least two specimens of the larynx of the pig or sheep, though the former is more like the human, and so the better on the whole. A case of dissecting instruments is not essential; a sharp pocket-knife will serve the purpose. In order that the student may have a clear idea of the cartilages, all the soft tissues must be cut or sc.r.a.ped away. It is necessary to exercise great care, or the membranes connecting the cartilages together will be cut through; and on the other hand, unless the work in the neighborhood of the arytenoids be cautiously done, these cartilages may be injured, and it is most important that their swivel-like action and their relations to the true vocal bands be observed. The glottic c.h.i.n.k can be seen from above or below, and should be observed from both view-points. Its margins are formed by the true vocal bands.
Then, with the figures before him, the student should endeavor to isolate each of the muscles described. The muscles can always be recognized by their red color, but it is to be remembered that those on the inner surface of the larynx, such as the crico-arytenoid, are covered with mucous membrane, which after death is very pale. This can by careful dissection be removed, and if in doing this a small pair of forceps be employed, the work will be greatly facilitated. One must be very skilful indeed if he would get all the muscles "out," or well exposed to view as individuals, on a single specimen. Likely several will be required before entirely satisfactory results are reached, but these are well worth all the time and labor required. The action of the muscles can in some measure be demonstrated by pulling on them in the direction of their loosest attachment, though it must be confessed this is much more difficult in the case of most of the muscles of the larynx than in those of other parts of the body.