THE VOICE.
586. The beautiful mechanism of the vocal instrument, which produces
every variety of sound, from a harsh, unmelodious tone, to a soft,
sweet, flute-like sound, has, as yet, been imperfectly imitated by
art. It has been compared, by many physiologists, to a wind, reed, and
stringed instrument. This inimitable, yet simple instrument, is the
_Lar'ynx_.
587. Incidentally, the different parts of the respiratory organs, as
well as the larynx, are subservient to speaking and singing. The
tongue, nasal passages, muscles of the fauces and face, are agents
which aid in the intonation of the voice.
ANATOMY OF THE VOCAL ORGANS.
588. The LARYNX is a kind of cartilaginous tube, which, taken as a
whole, has the general form of a hollow, reversed cone, with its base
upward toward the tongue, in the shape of an expanded triangle. It
opens into the pharynx, at its superior extremity, and communicates,
by its inferior opening with the trachea. It is formed by the union of
five cartilages, namely, the _Thy'roid_, the _Cri'coid_, the two
_A-ryt-e'noid_, and the _Ep-i-glot'tis_. These are bound together by
ligaments, and moved by muscles.
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586. What is said of the structure of the vocal instrument? With what
instrument have physiologists compared it? What is the vocal
instrument called? 587. What organs are called into action in speaking
beside the larynx? 588-596. _Give the anatomy of the vocal organs._
588. Describe the larynx. Name the cartilages that form the larynx.
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589. The THYROID CARTILAGE is the largest of the five, and forms the
prominence in the front of the neck, called _Po'mum A-da'mi_, (Adam's
apple.) It is composed of two parts, and is connected with the bone of
the tongue above, and with the cricoid cartilage below.
590. The CRICOID CARTILAGE takes its name from its resemblance to a
ring. It is situated below the thyroid cartilage, it is narrow in
front, broader at the sides, and still broader behind, where it is
connected with the thyroid cartilage. Below, it connects with the
first ring of the trachea.
[Illustration: Fig. 102. A side view of the cartilages of the larynx. *
The front side of the thyroid cartilage. 1, The os hyoides, (bone at the
base of the tongue.) 2, The ligament that connects the hyoid bone and
thyroid cartilage. 3, 4, 5, The thyroid cartilage. 6, The cricoid
cartilage. 7, The trachea.]
[Illustration: Fig. 103. A posterior view of the cartilages and ligaments
of the larynx. 1, The posterior face of the epiglottis. 3, 3, The os
hyoides. 4, 4, The lateral ligaments which connect the os hyoides and
thyroid cartilage. 5, 5, The posterior face of the thyroid cartilage. 6,
6, The arytenoid cartilages. 7, The cricoid cartilage. 8, 8, The junction
of the cricoid and the arytenoid cartilages. 12, The first ring of the
trachea.]
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589. Describe the thyroid cartilage. 590. From what does the cricoid
cartilage derive its name? Where is it situated? Explain fig. 102.
Fig. 103.
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591. The ARYTENOID CARTILAGES are small triangular bodies placed upon
the back part of the cricoid cartilage. They are connected with the
thyroid cartilages, by four ligaments, called _Vo'cal Cords_.
592. The EPIGLOTTIS is fibro-cartilaginous, and is placed behind the
base of the tongue. In shape it resembles a leaf of parsley.
593. The VOCAL CORDS, or ligaments, are formed of elastic and parallel
fibres, enclosed in a fold of mucous membrane. They are about two
lines in width, and pass from the anterior angle of the thyroid
cartilage, to the two arytenoid cartilages. The one is called the
superior, and the other the inferior vocal ligament. The cavity, or
depression between the superior and inferior ligament, is called the
_ventricle_ of the larynx. The aperture, or opening between these
ligaments, is called the _glot'tis_, or _chink of the glottis_. It is
about three fourths of an inch in length, and one fourth of an inch in
width, the opening being widest at the posterior part. This opening is
enlarged and contracted by the agency of the muscles appropriated to
the larynx.
[Illustration: Fig. 104. An ideal, lateral section of the larynx. 1, 1,
The upper vocal cords. 2, 2, The lower vocal cords. 3, 3, The glottis. 4,
4, The ventricles of the larynx.]
[Illustration: Fig. 105. A vertical section of the larynx. 2, The os
hyoides. 4, The apex of the epiglottis. 7, The superior vocal ligament.
9, The ventricle of the larynx. 10. The lower vocal ligament. 11, The
arytenoid cartilage. 12, 13, The cricoid cartilage. 14, The trachea. 18,
The oesophagus.]
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591. Describe the arytenoid cartilages. 592. What is said of the
epiglottis? 593. Give the structure of the vocal cords. Where is the
ventricle of the larynx? Where is the glottis situated? What is
represented by fig. 104? Explain fig. 105.
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[Illustration: Fig. 106. A view of the larynx from above, showing the
vocal ligaments. 1, The anterior edge of the larynx. 4, The posterior
face of the thyroid cartilage. 5, 5, The arytenoid cartilages. 6, 6, The
vocal ligaments. 7, Their origin, within the angle of the thyroid
cartilage. 9, Their termination, at the base of the arytenoid cartilages.
8, 10, The glottis.]
594. The larynx is connected by muscles with the sternum, oesophagus,
base of the skull, hyoid bone, lower jaw, and tongue. This organ is
supplied with a large number of blood-vessels, and it likewise
receives nerves from the sympathetic system, and two large nerves from
the tenth pair. The number and size of the nervous filaments
distributed to the mucous membrane of the larynx, render it more
sensitive than any other portion of the respiratory organs.
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How is the glottis enlarged or contracted? Explain fig. 106. 594. By
what means and to what organs is the larynx connected? Why is the
larynx more sensitive than other parts of the respiratory organs?
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595. The larynx is much more developed and prominent in man than in
woman. In the former, the anterior angle of the thyroid cartilage is
acute, while in the latter it is rounded, and the central slope of the
superior border of the same cartilage is less deep, and the epiglottis
smaller and less prominent, than in man.
596. The difference in the formation of the larynx in infancy is less
striking; but at a later period, it is more developed in the male than
in the female. It is very remarkable that this increase is not
progressive, like that of other organs, but, on the contrary, develops
itself at once at the period of puberty.
PHYSIOLOGY OF THE VOCAL ORGANS.
597. In the formation of the voice, each part already described
performs an important office. The cricoid and thyroid cartilages give
form and stability to the larynx; the arytenoid cartilages, by their
movement, vary the width of the glottis. The epiglottis is flexible
and elastic. When it is erect, the chink of the glottis is open, as in
inspiration; when depressed, as in swallowing food and drink, it
covers and closes this aperture. It prevents the introduction of
articles of food into the trachea, and probably modifies sound as it
issues from the glottis.
598. The muscles of the neck elevate and depress the larynx; the
muscles of the larynx increase or diminish the width of the glottis;
at the same time, the vocal cords are relaxed or tightened, while the
muscles of the face open and close the mouth.
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595. What difference between the formation of the larynx of the female
and that of the male? 596. Does this difference exist in childhood? Is
its development progressive? 597-600. _Give the physiology of the
vocal organs._ 597. Which cartilages give stability and form to the
larynx? Which vary the width of the glottis? What is the function of
the epiglottis? 598. What effect have the muscles of the neck upon the
larynx? The use of the muscles of the larynx?
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599. The elasticity of the ribs and the contraction of the abdominal
muscles diminish the cavity of the chest, and the air, in consequence,
is pressed from the air-cells into the bronchial tubes and trachea. It
then rushes by the vocal cords, and causes a peculiar vibration, which
produces _sound_.
_Observations._ 1st. Experiments have satisfactorily shown that the
vocal cords are the principal agents in the formation of the voice.
The tongue, which many have supposed to be the most important organ in
speaking, is not essential to sound. In several instances it has been
removed, and the persons thus mutilated could speak with fluency.
2d. When the vocal cords are ulcerated, or inflamed, however slightly,
as in sore throat produced by a cold, the voice will be changed. The
loss of speech among public speakers is generally produced by a
relaxation of the vocal ligaments. Hence, bronchitis is a misnomer for
this affection.
600. Sound is varied by the velocity of the expelled current of air,
and the tension of the vocal ligaments. The size of the larynx, the
volume and health of the lungs, the condition of the fauces and nasal
passages, the elevation and depression of the chin, the development
and freedom of action of the muscles which are attached to the larynx,
the opening of the mouth, the state of the mind, and general health of
the system, influence the modulations of sound.
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What effect has the combined action of these muscles? 599. How is
sound produced? What have experiments shown? What effect has disease
of the vocal ligaments upon the voice? 600. How is sound varied?
Mention other conditions that contribute to the modulation of sound.
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