Are Thou Troubled,
Music will come Thee,
Art Thou Weary,
Rest shall be Thine,
Music, music,
Source of all gladness,
Heals thy sadness,
At her shrine,
Music, music, ever divine,
Music,
Music calleth,
With voice divine.
Here is the organ that is seen in the laryngeal mirror.
It is a framework of cartilages at the top of the trachea or windpipe.
In it are structures which form a valve through which the breath passes.
We should have a clear concept of these cartilages and muscles.
This is a male larynx suspended from the hyoid bone
and at the top of the section of the trachea.
The most important cartilages are the thyroid,
the cricoid, the two arytenoids, and the epiglottis.
Let us build up a larynx part by part to study its structure and function.
Here is a section of the trachea.
It is composed of rings of cartilage which keep it open for the passage of air.
However, it is flexible and dispensable,
and also the cartilaginous rings are incomplete at the back and are closed by muscular and membranous tissue.
We shall place this section of the trachea on this spindle.
This is the cricoid cartilage.
It is the only cartilage in the larynx which is a complete ring closed at the back.
It is shaped somewhat like a signet ring being smaller in front and having a large plate at the back.
Its upper edge forms an oval.
The cricoid is found at the top of the trachea.
We have attached the cricoid cartilage to our spindle with two nails.
Notice that there are four facets for the articulation of other cartilages.
Two are concave.
One.
Two.
These are for the thyroid cartilage.
Two are convex with oval outlines.
One.
Two.
These are for the arytenoid cartilages.
This is the left arytenoid cartilage.
It is roughly pyramidal in shape having three projections.
The one at the top is called the apex.
The large blunt one at the side is called the muscular process.
And we shall find that several muscles attach to it.
The smaller flexible pointed one extending to the front is called the vocal process
because the vocal ligament and vocalis muscle attach to it.
On the underside of the muscular process is a concave almost cylindrical facet for articulation with the cricoid.
Notice that it is here under the muscular process.
Let us put it in place.
It has two possibilities of movement which we shall call rocking and gliding.
It is held in place flexibly by a ligamentous capsule which is especially strong here.
The ligament anchors the arytenoid to the cricoid plate here in the middle.
Here is the rocking movement.
There is also a gliding movement along the slope of the oval shaped top of the cricoid.
Of course, arytenoids come in pairs, so let us have the right one also in place.
Now the two arytenoid cartilages are perched with the vocal processes pointing toward the front
and their muscular processes pitting the convex facets on the curving upper edge of the cricoid plate.
Ligaments hold them loosely and flexibly.
Here are the muscles that move the arytenoids in various ways.
The posterior cricoarytenoid muscles are these large ones which cover much of the cricoid plate.
They are called posterior because they are at the back and they are called cricoarytenoid
because they arise from the cricoid and are inserted in the arytenoids.
With attached threads we can simulate the action of these muscles.
We shall do the same with all the others as well.
When the posterior cricoarytenoid muscles contract,
they separate the arytenoids with a complex movement largely rocking.
Joining the arytenoid cartilages at the back are three interarytenoid muscles.
On the surface are two small inconspicuous muscles crossing each other to make a letter X.
They are called the oblique arytenoid muscles.
Beneath them, running from side to side, is a larger, much more powerful muscle
called the transverse arytenoid muscle.
When these muscles contract, they draw the arytenoids together.
The lateral cricoarytenoid muscles can now be seen.
They are called lateral because they are at the sides and cricoarytenoid because they arise
from the cricoid here and extend along the upper edge of this cartilage to be inserted
in the arytenoids.
Notice that these muscles attach to the muscular processes of the arytenoid cartilages.
When the lateral cricoarytenoid muscles contract, the muscular processes are drawn forward.
This results in an interesting adjustment of the vocal processes, which we shall see
better in another position.
We shall look down on these parts in much the same direction as they are seen in a laryngeal mirror.
We observe the movements of the arytenoids as each pair of muscles contracts and exerts its pull.
The posterior cricoarytenoid muscles separate the arytenoids with a rocking motion, and
the interarytenoids draw them together again with a rocking and upward gliding movement
so that the apexes meet.
The lateral cricoarytenoid muscles do this, rocking and gliding.
The gliding movement may have a rotating component around the upper or lower corners of the cricoarytenoid
facet.
We notice that the muscular processes are drawn forward and the vocal processes contact
each other.
When both the laterals and the interarytenoids contract, there is firm contact between the
arytenoid cartilages like this.
These movements will become more meaningful when we see the vocal folds in place.
For this we need a thyroid cartilage.
Here is the thyroid cartilage.
It has two wings fused at the front.
The wings are fused only at the bottom, and there is a notch above.
They are open at the back, and each wing has an upper horn and a lower horn.
The lower horns articulate with facets on the cricoid cartilage.
Now we have seen that the arytenoids are attached to the cricoid with a rocking and gliding articulation.
This is also true of the cricothyroid articulation.
The thyroid can rock with the point of articulation as its center thus.
It can also glide a little.
This is the cricothyroid ligament.
It prevents the cartilages from moving too far apart at the front.
Here are the cricothyroid muscles, so called because they arise from the cricoid cartilage
at the front and fan out toward the back to be inserted in the lower edge of the thyroid cartilage.
When the cricothyroid muscles contract, there is a combination of both the rocking and the
gliding of the thyroid cartilage.
They pull partly downward and partly forward.
These white bands are called the vocal ligaments.
They extend from the angle of the thyroid cartilage to the arytenoid cartilages.
One ligament is attached to each vocal process.
When the cricothyroid muscles are relaxed, the vocal ligaments are slack.
When the cricothyroid muscles contract, the ligaments are stiff.
Under these conditions, at very high pitches, the vocal ligaments function almost independently
of the vocal muscles, rather like strings.
We notice that the action of the cricothyroid muscles tenses the ligaments but does not
bring them together.
These are the thyroarytenoid muscles.
They arise from the thyroid cartilage and are inserted in the arytenoid cartilages.
They are complex and are composed of several bundles of muscle fiber.
The bundles which lie beside the vocal ligaments and which are loosely connected to them are
the internal thyroarytenoid muscles.
They attach in part to the vocal processes and extend toward the muscular processes and
form the body of the vocal folds.
The internal thyroarytenoid muscles are also called the vocalis muscles.
More colloquially, these structures, consisting of the vocalis muscles, the vocal processes,
and the vocal ligaments, are called the true vocal cords.
Lying beside the internal thyroarytenoids are the external thyroarytenoid muscles, part
of which has been removed and does not show in our picture at this moment.
They attach to the muscular processes and all along the outside edges of the arytenoid
cartilages up toward the apex.
Let us observe the functions of the adjusting muscles with reference to the vocal folds.
Moving the vocal folds away from the center is called abduction.
Moving the vocal folds toward the midline is called adduction.
When the posterior cricoarytenoids contract, the arytenoid cartilages are separated and
the space between the vocal folds is large.
This space is called the glottis.
In breathing, the glottis is open.
The posterior cricoarytenoids are the chief abductor muscles.
The interarytenoid muscles, on the other hand, are adductory.
When they contract, the apexes of the arytenoids are drawn together.
Posterior cricoarytenoid, interarytenoid.
The lateral cricoarytenoid muscles bring the vocal processes toward midline.
Here is what happens when they work alone.
We see that the lateral cricoarytenoid muscles exert a leverage so that the vocal processes
are pressed together.
We shall call this medial compression.
But to close the glottis completely, we must contract both the lateral cricoarytenoid muscles
and the interarytenoid muscles.
Posterior lateral interarytenoid.
Posterior lateral interarytenoid posterior.
When the thyroarytenoid muscles contract, they reduce the distance between the angle
of the thyroid and the arytenoid cartilages, and the vocal ligaments are slackened.
On the other hand, when the thyroid moves forward, away from the arytenoids, the vocal
folds are stretched.
It is the cricothyroid muscles that do this.
This action stretches the vocal folds.
We shall call it longitudinal tension.
We might expect longitudinal tension to close the glottis, but instead there appears a narrow
opening even though the interarytenoid muscles are contracting.
Adequate medial compression will close this chink.
Here is an interior view of the larynx.
The thyroid cartilage has been cut through here.
Here is the front of the cricoid, also cut through, and here is the plate.
It has been necessary to drive two nails through the cricoid.
This is the arytenoid cartilage.
Here is what happens when the posterior cricoarytenoid muscle contracts.
Now the lateral cricoarytenoid.
Posterior lateral posterior lateral.
This is the vocal ligament.
It is the thickened upper edge of a membrane which strengthens the underside of the thyroarytenoid
muscles.
This membrane is called the conus elasticus.
Its lower edge attaches to the upper edge of the cricoid cartilage, and it includes
the cricothyroid ligament.
As we see the specimen now, there is no longitudinal tension, and so the vocal fold is loose and
thick.
The cross section of the vocal fold is determined by the thickness of the vocalis muscle when
the longitudinal tension is very small.
We shall call the tone produced by such an adjustment chest voice.
Now as longitudinal tension is applied, see how the vocal fold thins out.
This thin edge is really the vocal ligament.
When longitudinal tension is great, the shape of the vocal fold is largely determined by
the vocal ligament.
We shall call this the falsetto adjustment.
As a matter of convenience, the action of the cricothyroid muscle is usually conceived
as causing the thyroid cartilage to rock on the cricoid cartilage.
It is shown thus in our film.
However, if the thyroid is held motionless, the cricoid must rock.
Thus.
This is more nearly what happens in life.
However, for the highest tones of the voice, when the muscles of the throat lift the larynx,
the larynx as a whole is tilted.
The vocal folds are stretched in any case, but the picture in the laryngeal mirror is
different.
For the lowest pitches, when the cricothyroids are not contracting, the arytenoids obscure
the view of the back part of the folds.
This position gives the best view.
We are now going to apply air to our specimen and observe the vibration of the vocal folds.
It will be necessary to remove the horns of the thyroid to avoid interference with our
thread.
There is no longitudinal tension, so the vocal folds are loose and thick, and the sound will
be that of chest voice.
The glottis opens by contraction of the posterior cricoarytenoid muscles.
Now the posterior cricoarytenoid muscles relax.
Listen to the tone when both the interarytenoid muscles and the lateral cricoarytenoid muscles
contract.
It is necessary to use a contact microphone so there are small differences in loudness
and quality between our soundtrack and the airborne sound.
It is possible to slow this vibration, apparently, by means of stroboscopic light and a Delta
F generator so that one cycle of vibration will last about one second on the screen.
This makes it possible for us to observe in detail the vibrational pattern of chest voice.
Let us note some of the distinguishing characteristics.
We have already noted that this vibrational pattern is the result of having little or
no longitudinal tension.
Very little elongation of the vocal folds.
The vocal ligaments are slack, and the vocal folds are thick.
The amplitudes of the vibrations are great.
That is, the vocal folds move a rather large distance away from the midline.
The glottis opens rather widely each time.
Because of the thickness of the folds, the glottis closes firmly and remains closed an
appreciable time in each vibration so that air pressure builds up below and fairly bursts
out.
Each puff of air opens the glottis almost explosively.
The air presses them apart at the bottom first and bubbles through to the top.
The glottis also closes at the bottom first.
This is called a vertical phase difference.
All of these characteristics make chest voice suitable for low frequencies, comparatively
loud, and rich in harmonic partials.
Let us listen to it again.
We shall vary one factor at a time, keeping the others constant.
First, only the interarytenoid muscles contract.
We observe no vibration, but when we suddenly apply a spurt of air, it will start.
Now let us contract only the lateral cricoarytenoid muscles.
The tone is rather breathy because air is escaping between the arytenoids.
The action of the interarytenoid muscles will close this chink.
With the increased efficiency of the glottis, we can reduce the flow of air.
Now with the interarytenoids firmly contracted, let us increase medial compression, other
factors constant.
Now let us reduce medial compression and then increase air flow, other factors constant.
Now let us reduce air flow and then increase longitudinal tension, other factors constant.
We observe that intensifying any one factor while keeping the others constant causes the
pitch to go up and the loudness to increase.
However, unless medial compression increases at the same time, it is impossible to increase
longitudinal tension very greatly in chest voice.
Let us keep in mind the thickness of the vocal folds.
We have been observing their behavior when they are like this, but now let us apply longitudinal
tension.
The vocal folds become thin and tense.
The sound they will produce is a falsetto tone.
At large degrees of longitudinal tension, we can expect small amplitude of movement.
It is difficult to move the vocal ligaments away from the midline.
Let us apply adequate medial compression and air and observe the vibration under normal
light.
This is what the stroboscope shows.
It seems to be at the same frequency as chest voice, but this is the effect of the Delta
F generator.
Actually, it is over two octaves higher than chest voice.
These are the distinguishing characteristics.
There must be great longitudinal tension and with it, medial compression will also be needed.
The longitudinal tension will lengthen the vocal folds.
Consequently, the vocal ligaments will be tense.
Even more tension can be added in this register after the ligaments have been stretched to
maximum length.
The vocal folds, as we have seen, are thin.
Because of the great tension, the amplitudes are small.
That is, the glottis does not open as widely as in chest voice.
Also, the glottis is not firmly closed in each vibration.
Often in falsetto, the glottis does not close completely.
Because the vocal folds are thin, vertical phase difference is negligible.
That is, there is no such thing as the glottis opening at the bottom first and then at the
top.
Let us listen once more.
First, only the interarytenoid muscles contract.
We observe no vibration, even if we give a sudden spurt of air.
Now, let us contract only the lateral cricoarytenoid muscles.
Now we add the contraction of the interarytenoid muscles.
We observe that for the best falsetto, both contraction of the interarytenoids and medial
compression are needed.
Now we have only the interarytenoids contracted and we shall gradually add medial compression
until the tone begins and then increases in volume and rises in pitch.
Now we reduce medial compression and increase airflow, other factors constant.
Now we reduce airflow and, keeping it constant, increase still more the longitudinal tension,
which is already great.
Between these extreme adjustments, chest and falsetto, we can produce intermediate types
of vibration corresponding to intermediate degrees of longitudinal tension.
This can be seen in the excised larynx here and, of course, also in the living larynx.
Now, with adequate medial compression, let us begin in the upper part of chest voice
and increase longitudinal tension.
Now, we go back down.
Before we observe the living larynx, however, we must familiarize ourselves with some more
parts of the larynx.
Our study, up to this point, has concerned itself with the most important structures
of phonation, trachea, cricoid, thyroid, cricothyroid muscles, arytenoids, posterior cricoarytenoid
muscles, interarytenoid muscles, lateral cricoarytenoid muscles, thyroarytenoid muscles consisting
of internal thyroarytenoid muscles, or vocalis muscles, and the external thyroarytenoid muscles.
There are structures above which are less important than these in phonation, though
they serve other purposes.
We should add them.
The external thyroarytenoid muscles extend upward somewhat higher than the internals,
and some of the fibers are found in a fold of tissue above which hangs over the internals
and forms a pocket on each side.
These pockets are called the laryngeal ventricles of morgani, and the folds which form them
are called the ventricular folds, or colloquially, false vocal cords.
There is a leaf-shaped cartilage called the epiglottis.
It is attached to the thyroid cartilage at the notch and is a lid for the glottis.
It is pulled over the glottis when one swallows.
This movement is caused by the action of muscles that extend between the epiglottis and the
arytenoid cartilages.
This is called the collar of the larynx.
It is formed by the epiglottis at the front, the arytenoid cartilages at the back, joined
by the areopiglottic folds which contain muscular fibers.
Actually, these fibers are continuations of the oblique arytenoid muscle.
Altogether we have a purse-string effect for closing the top of the larynx to keep foreign
materials out of the windpipe.
Here in the areopiglottic folds near the arytenoid cartilages are two lesser cartilages which
serve no special function except perhaps to stiffen the collar somewhat.
They are called the cuneiform cartilages of Risberg.
Here is the interior of our specimen as it is now.
The epiglottis has been sectioned.
Here is the areopiglottic fold containing the cuneiform cartilage of Risberg.
Here is the ventricular fold and below it the ventricle of Morgani.
Joining all these parts is a membrane which contains a number of glands for lubricating
the larynx.
It is called the quadrangular membrane which roughly describes its shape.
One of the cartilages we have considered is the hyoid bone.
It is U-shaped having a central body and two horns, one on each side.
The hyoid bone is called the tongue bone because the tongue arises from it.
It is suspended from the base of the skull and from the jaw bone by numerous muscles
and still other muscles extend from it to the breast bone and other attachments below
the larynx.
These muscles position the hyoid bone in the throat, high, low, forward or back and since
the larynx is suspended from the hyoid bone, these muscles which move the hyoid bone may
under certain conditions exert tension upon the larynx and the vocal folds within.
The larynx is suspended from the hyoid bone in this manner.
There is a ligament in front called the hyothyroid ligament.
There is a rather large muscle on each side called the hyothyroid muscle and between the
hyoid bone and the thyroid cartilage is a membrane called the hyothyroid membrane.
On each side there are two main nerves which supply the larynx, both of which come from
the vagus nerve.
The upper one is called the superior laryngeal nerve and the lower one is called the inferior
laryngeal nerve.
The superior nerve forks into an internal and an external branch on each side.
The external supplies the cricothyroid muscle.
The internal branch has several smaller branches passing through the hyothyroid membrane.
They contain mostly sensory fibers having endings in the upper mucous membrane of the
larynx.
The inferior laryngeal nerve is the upper ending of a large branch of the vagus called
the recurrent nerve.
There is one on each side coming up along the trachea and branching again to activate
all the muscles of the larynx except the cricothyroid.
These nerves also carry sensory fibers.
There is a connection between the superior and the inferior laryngeal nerves.
We are now going to see the larynx of a trained singer.
This is what the laryngeal mirror shows.
Here are the vocal folds whose edges are the vocal ligaments in the front part and the
vocal processes in the back part.
Paralleling the vocal folds are the ventricular folds here and here.
The upper parts which form the collar will be nearer the camera.
This makes them look large and not in perfect focus.
This is the apex of one arytenoid cartilage and this is the other.
The lumps in the edge of the collar on either side here and here are made by the cuneiform
cartilages of Risberg.
Here is the epiglottis and above it the base of the tongue.
Let us observe chest and mid-voice.
Let us move very close to the vocal folds.
And now some pictures of an untrained, sensitive subject with asymmetrical vibration.
But now the train singer again.
And now some pictures of an untrained, sensitive subject with asymmetrical vibration.