THE SPECIAL VOICE-PRODUCING MECHANISM, THE LARYNX.
The larynx, or voice-box, is not the sole voice-producing apparatus,
as is often supposed, but it is of great, possibly the greatest,
importance. In describing the parts of this portion of the vocal
mechanism the author deems it wiser to use the terms commonly employed
by anatomists and physiologists, as others are awkward and inadequate.
Moreover, there is this great advantage in learning the technical
names of structures, that should the reader desire to consult a
special work on anatomy in reference to this or other important
organs, he will find in use the same terms as he has himself already
learned. Such are, as a matter of fact, not difficult to learn or
remember if one knows their derivation or other reason for their
employment. All the muscles of the larynx have names which are not
arbitrary but based on the names of the structures to which they are
attached, so that one has but to know their connections and the names
of the solid structures, which are few, to have a key to the whole
nomenclature.
When one is not using the voice the larynx is simply a part of the
respiratory apparatus, but when one phonates this organ assumes a
special function for which specific structures are essential. As
sound is caused by vibrations of the air, and these may be set up by
vibrations of the vocal cords, it may with absolute correctness be
said that the whole larynx exists for the vocal bands so far as
voice-production is concerned. Such a view renders the study of the
larynx much more interesting and rational; one is then engaged in
working out that solution of a problem which Nature has accomplished.
The vocal cords, we can conceive, might be either relaxed or
tightened, and lengthened or shortened, or both, and beyond that we
can scarcely understand how they might have been modified so as to be
effective in the production of sounds of different pitch. As a matter
of fact, these are the methods Nature has employed to accomplish her
purpose. For each vocal cord one fixed point, and only one, is
required. We know of only one method in use by Nature to cause
movement in living structures--viz., contraction, and muscle is the
tissue which above all others has that property; hence the movements
of the vocal cords are brought about by muscles. But both for the
attachment of the muscles and the vocal cords themselves solid,
relatively hard structures are required. Bone would prove too
unyielding, but cartilage, or gristle, meets the case exactly. The
entire framework of the larynx--its skeleton, so to speak--is made up
of a series of cartilages united together so as to ensure sufficient
firmness with pliability.
The cartilages have been named from their shape, as that appealed to
the original observers, and the terms employed are of Greek origin.
The largest and strongest is the _thyroid_ (_thureos_, a shield)
cartilage, which resembles somewhat two shields put together in front
without any visible joint, and open behind but presenting a strongly
convex surface externally, in front and laterally. "Front" (anterior)
and "back" (posterior) always refer in anatomy to the subject
described, and not to the observer's position. In observing another's
larynx the subject observed and the observer naturally stand front to
front, and it is impossible to see or touch the back of the larynx as
it is covered behind by the other structures of the neck.
This thyroid, the largest of the cartilages, is attached to the hyoid
or tongue bone above by a membrane, so that the whole larynx hangs
suspended from this bone by a membrane, though not by it alone, for
muscles are attached to it which also serve for its support. It is of
practical importance to remember that the larynx is free to a very
considerable extent, otherwise it would go ill with the voice-producer
in the vigorous use of the voice, not to mention the advantages of
mobility as well as pliability in the movements of the neck
generally.
[Illustration: FIG. 20 (Spalteholz). Shows the thyroid cartilage above
and the cricoid below both viewed from the side. The anterior surface
is turned toward the right.]
[Illustration: FIG. 21 (Spalteholz). A front view of FIG. 20.]
[Illustration: FIG. 22 (Spalteholz). The back or signet surface of the
cricoid or ring cartilage, to which several muscles are attached.]
[Illustration: FIG. 23 (Spalteholz). The cricoid cartilage, seen from
the side, and showing behind and laterally the articular or joint
surfaces by which it connects with the thyroid below and the arytenoid
cartilage above.]
[Illustration: FIG. 24 (Spalteholz). Shows the arytenoid cartilages,
the most important of all the cartilages of the larynx, inasmuch as to
the part termed "vocal process" the vocal band is attached on each
side. The movements of the vocal bands are nearly all determined by
the movements of these cartilages, which have a swivel-like action. In
the above the front surfaces are turned toward each other.]
The _cricoid_ (_krikos_, a signet-ring) is the cartilage next in size.
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 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.
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.
[Illustration: 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.]
[Illustration: 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.]
[Illustration: 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.]
[Illustration: 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 passes 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 chink.
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 passing like a plumb-line from the middle plane of the head,
let us suppose, downward just in front of the larynx.
[Illustration: 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 space 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 illustration 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.
[Illustration: 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 assumed when the
muscle has contracted.]
[Illustration: FIG. 31 (Spalteholz). View of the larynx as looked at
from above. The illustration 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.]
[Illustration: 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 space 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 class, 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 bass, 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 coöperation
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 coöperate, 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
[Illustration: 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 accumulation 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.
[Illustration: FIG. 33 (Spalteholz). Shows various structures, and
especially well the false and the true vocal bands, with the space
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 space is a natural result of the existence of
two pairs of vocal bands in such close proximity.]
[Illustration: 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 bass," 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 illustrations 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 illustrates 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 scraped 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 chink 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.
Should the specimens be very successfully dissected, it may be worth
while to keep them for future observation, in rather weak alcohol (40
per cent.), in, say, a preserve jar.
All examinations of the vocal bands may leave the observer
disappointed; he may fail to realize, most likely, how such wonderful
results can be accomplished by structures so simple as those he sees
before him. But when the laryngoscope is brought into use, then comes
a revelation. This instrument will be described in the next chapter.
HYGIENE.
Some of the hygienic principles involved have already been referred to
and illustrated, and others follow from the facts already set forth.
It is very important for the voice-user to bear in mind that his
larynx is a part of the respiratory tract, and that the whole of this
region and the entire digestive tract, part of which is common to
both, are lined with mucous membrane. If the nose be affected with
catarrh, the throat does not usually long escape; and if the back of
the mouth cavity (_pharynx_) be disordered, the vocal bands and other
parts of the larynx are almost sure to be involved more or less.
The condition of the stomach is reflexly, if not by direct continuity
through the mucous membrane, expressed in the throat generally; hence
as experience shows, the voice-user cannot exercise too great care as
to what and how much he eats, especially before a public appearance.
He must know himself what best suits him, in this regard, to a degree
that is necessary for few others.
When singing, more blood is sent to the organs used, hence the great
danger of that excess of blood being retained in the parts too long,
as might easily happen from pressure about the neck, etc. It is
scarcely necessary to point out that draughts, cold rooms, etc., will
also determine the blood from the skin inward, and set up that
complicated condition of multiform evils known as "a cold." The
obvious principle of prevention lies in keeping the body, and
especially the neck, shoulders, and chest, warm after using the vocal
organs in any way in public. To hand the singer a wrap after leaving
the platform is always wise, and the judicious friend will see that
conversation is not allowed, much less forced on the possibly
breathless and wearied voice-user--a precaution that is probably more
honored in the breach than in the observance, for in this as in other
cases one's friends are sometimes his worst enemies.
SUMMARY.
The larynx is the most important organ in voice-production, and
consists of cartilages, muscles, the vocal bands, true and false,
membranes and ligaments, folds of mucous membrane, etc. It is situated
between the hyoid (tongue) bone above and the trachea below. The
cartilages are the (1) epiglottis, (2) thyroid, cricoid, arytenoid,
the two small, unimportant cornicula laryngis, or cartilages of
Santorini, surmounting the arytenoids, and the two cuneiform, or
cartilages of Wrisberg, in the folds of mucous membrane on each side
of the arytenoids.
The muscles are attached to the main cartilages. In addition to the
muscles that are concerned with the movements of the vocal bands,
others that hold the larynx in place or raise and lower it are
attached _externally_ to these, especially to the large thyroid
cartilage. The epiglottis, the false vocal cords, the true vocal
cords, and the thyro-arytenoid muscles are attached to the interior
anterior surface of the thyroid in this order from above down.
The false vocal bands have no direct function in phonation. _The whole
larynx, so far as phonation is concerned, may be said to exist for the
true vocal bands._ They are attached close together to the internal
and anterior surface of the thyroid in front and to the lower anterior
angles (vocal processes) of the arytenoids behind. Between the false
vocal bands above and the true vocal bands below there is a cavity
(the ventricle of Morgagni). The false vocal bands are protective, and
approximate closely during coughing, swallowing, etc.
It is very important to note that the arytenoid cartilages move freely
on their base, swivel-like, so that nearly all the changes effected in
the movements and tension of the vocal bands are brought about through
alterations in the position of these cartilages; and this implies that
all the muscles concerned are attached to them. From above down, in
front, the order of structures is as follows:
Hyoid bone.
Membrane.
Thyroid cartilage.
Membrane.
Cricoid cartilage.
Trachea.
The hyoid bone is not a part of the larynx, but from it the larynx is
suspended. The bone itself gives attachment to the muscles of the
tongue. The glottis is the chink between the true vocal bands.
The muscles of the larynx may be divided into the following: (1) Those
that open and those that close the glottis; (2) those which regulate
the tension of the vocal bands. The latter include the (_a_)
crico-thyroids, which tense and elongate them, (_b_) thyro-arytenoids,
which relax and shorten them. The crico-thyroid may be considered the
most important muscle of phonation, because it is so much used and so
effective. By its action the cricoid is pulled up in front and down
behind, so that the arytenoids are drawn back, and thus the vocal
bands tensed and lengthened. The lateral crico-arytenoids and the
thyro-arytenoids have the opposite effect--_i.e._, they relax and
shorten the vocal bands; hence when they come into play a new register
begins. The thyro-arytenoids, attached along the whole length of the
vocal bands externally, have a very important but not well-understood
action in the production of the higher tones, and probably also of the
falsetto.
The whole larynx is lined with mucous membrane, that covering the true
vocal bands being very thin. The false vocal bands are made up chiefly
of mucous membrane; the true vocal bands abound in elastic tissue. The
larynx rises during the production of high tones, and during
phonation its vibrations may be felt, as also those of the chest.
_Practical._
1. Feel in your own person the parts of the larynx, etc., from above
down.
2. Note the vibration of the larynx when a vowel is spoken or sung. A
similar vibration of the chest walls may be felt by the hands laid
over them.
3. Note the change of position of the larynx in singing a scale.
4. Dissect a pig's or sheep's pluck and some specimens of the larynx.
[Illustration: FIG. 35. These three figures illustrate perhaps more
clearly the _action_ of the muscles indicated FIGS. 26-34.
The arrows show the direction of the pull of the muscles. The result
of this action is the new position of the cartilages and vocal bands,
which is shown by red outlines. The muscle is also depicted in red.
The heavier outer rim is to indicate the thyroid cartilage. By
comparing the upper and the lowest figure it will be seen that they
are opposites. Of course, in phonation the vocal bands are never so
much separated as shown in the illustrations. Rather does the lower
figure indicate a case of extreme separation due to a very deep
inspiration. However, these illustrations are merely diagrams meant to
indicate in a general way the manner of the working of parts. For
exact pictures of the vocal bands and related parts, see Chapter
VII.]