The larynx may be regarded as the funnel-shaped termination
of the trachea. It enlarges upward and is composed of various
cartilages more or less mobile, connected by ligaments and
moved by muscles. The exterior of the larynx is formed by the
I. Thyroid cartilage.
II. Cricoid cartilage.
The cartilages in the interior are:
I. The Arytenoid cartilages.
II. Cartilages of Wrisberg.
III. Cartilages of Santorini.
IV. Cuneiform cartilages.
To the cartilages of the larynx must be further added the
Epiglottis, with the little cartilage at the centre of its
inner side.
1. The _thyroid cartilage_ is the largest cartilage of the larynx,
and consists of two four-cornered cartilaginous plates held together
in front and diverging behind; the anterior borders are convex, and
consequently where the two plates meet in front they form an upper
and a lower notch or slit. The posterior angles of this cartilage
extend into the so-called horns of the _thyroid cartilage_. At
the upper horns are ligaments attached, which form the connection
between the hyoid bone and the larynx, while the lower horns serve
to join the thyroid to the cricoid cartilage. In females and boys
the angle formed by the two plates of the _thyroid cartilage_ is
obtuse. In the male sex at a certain period the larynx changes
its shape, and the plates of the _thyroid cartilage_ then form an
acute angle, which is visible on the outside of the throat, and is
popularly known as the _Adam's apple_. At this time the diameter
of the male larynx becomes a third larger than that of the female
larynx, and in consequence the voice is lower, and its different
registers are more enlarged in compass.
2. The _cricoid cartilage_ resembles in shape a seal ring;
its broader side is situated posteriorly between the lower
horns of the _thyroid cartilage_, and it is connected by its
lower edges immediately with the upper edge of the first ring
of the trachea. From its side at the back part project two
rounded surfaces, which give attachment to the _arytenoid
cartilages_.
3. The _arytenoid cartilages_ are two small but very mobile bodies
in the form of three-cornered pyramids. The base of the pyramid
rests upon the before-mentioned rounded surface at the back of the
upper border of the _cricoid cartilage_; one of its sides turns to
the front, the two others to the back and outwards. The surfaces
between the anterior and postero-interior corners are accordingly
turned towards one another. The surface posteriorly is concave,
and affords space for a part of the _arytenoid muscle_; the inner
surface is smooth, and forms, during quiet breathing, a part of
the lateral wall of the larynx; the anterior surface is rough and
irregular, and to it adhere the _vocal chords_, the _thyro-arytenoid
muscle_, the _lateral and posterior crico-arytenoid muscles_, and
upon these the bases of the _cuneiform cartilages_. The _arytenoid
cartilages_ are lengthened at their summits by two little
pear-shaped elevations, the _cartilages of Santorini_ (called
_apophyses_ in Garcia's observations), which are connected with
them by ligamentous fibres, and extend with them some distance
into the larynx.
4. The _cartilages of Wrisberg_ are described by Hyrtl as slight
elevations upon the front or anterior edge of the _arytenoid
cartilages_, inclining towards the interior, and, like all
parts of the larynx, covered by the mucous membrane.
5. The _cuneiform cartilages_ (as Wilson names them) are two
long, slender cartilaginous laminæ which become somewhat broader
at both ends. These cartilages, with their base, rest in the
middle of the anterior surface of the _arytenoid cartilages_,
and reach to the middle of the vocal chords, by which they are
enveloped. The action of these cartilages renders possible the
production of the head tones, but they are not found in every
larynx. The fact that they are oftener found in the female
larynx than in that of the male, and that the male larynx is
mostly used in scientific investigations, as it is larger and
more easily dissected, may be the reason why up to the present
time no mention is made of them either in German or French
manuals. They are sometimes referred to as cuneiform cartilages,
or confounded with the cartilages of Wrisberg, probably because
it seemed unaccountable that these important bodies should so
long have escaped the attention of anatomists.
From the anterior surface of the _arytenoid cartilages_, extending
towards the centre of the inner wall of the _thyroid cartilage_,
running diagonally through the cavity of the larynx, are stretched
the two pairs of chords already more than once mentioned--the vocal
chords, consisting of folds of the mucous membrane which envelopes
the whole larynx. The two lower of these chords, the vocal chords
strictly so called, into which the _cuneiform cartilages_ project
and through which the interior thyro-arytenoid muscles run, have
their points of attachment at the _arytenoid cartilages_, somewhat
lower than the upper pair. Each of these parallel pairs of chords
form between their lips a slit running antero-posteriorly. The slit
of the upper pair is opened in the shape of an ellipse; that of the
lower pair, the glottis, is very narrow. As the upper chords have
their point of attachment posteriorly and higher, they form with
the lower chords two lateral cavities, the ventricles.
The two pairs of chords, therefore, are the free interior edges
of the membrane, covering the whole larynx and extending into it
to the right and the left. Only the lower vocal chords serve
directly for the generation of tones. More or less stretched and
presenting resistance to the air forcibly expired from the lungs
through the trachea, they are thus made to vibrate. The upper or
false vocal chords do not co-operate with them to generate tone,
but like all the remaining parts of the mouth and throat belong
to the resonance apparatus of the voice, to which also appertains
the back part of the mouth, the _pharynx_, over the œsophagus,
the throat, or gullet. This is separated from the anterior cavity
of the mouth by the palate, which is a curtain formed by the
mucous membranes of the cavity of the mouth, and the centre of
which forms the pendent uvula.
Above the œsophagus, immediately over the palate, lie close
together, and separated only by a very thin osseous partition,
the two posterior nasal orifices. These serve as passages for
the air during inspiration and expiration; they are likewise
considered as belonging to the resonance apparatus.
Upon both sides of the cavity of the mouth, between the two
wings of the palate, lie the tonsils, two glandular bodies,
which separate the sides of the cavity of the mouth from the
_pharynx_. The anterior cavity of the mouth, which is separated
from the nasal cavities by the palate, requires no description,
as every one can acquaint himself with its structure in his own
person and in others. Upon its formation, as well as upon the
position of its different parts and upon the character of those
parts of the larynx and of the cavity of the mouth which have
been described as the resonance apparatus, the difference in
the fulness and timbre of tones depends.
The _epiglottis_ is fixed at the anterior portion of the
larynx, at the root of the tongue, within the angle formed by
the two surfaces of the thyroid cartilage. It is a very elastic
fibro-cartilage, freely moving in a posterior direction. Its
color is yellowish and its general form that of a spoon; its
upper surface is covered with a multitude of little mucous
glands set in shallow cavities. In the downward passage of food
the _epiglottis_ covers the upper orifice of the larynx like
a valve, over which the food passes into the œsophagus or
gullet, without being able to enter the larynx and the trachea.
In the centre of its interior side there is a little rounded
cartilage, movable in every direction, which has as yet no
name. Czermak mentions it first in his observations with the
laryngoscope. In the male larynx, after the voice has altered,
the cartilages become more or less ossified and gradually
harden with increasing age. The cartilages of the female
larynx, with rare exceptions, usually continue with little or
no change. The muscles, by which the movements of the larynx
are effected, are:
I. The posterior crico-arytenoid.
II. The lateral crico-arytenoid.
III. The crico-arytenoid.
IV. The thyro-arytenoid.
V. The arytenoid.
VI. The internal thyro-arytenoid.
In late works upon laryngoscopy the different muscles of the
larynx are variously designated and divided. Bataille terms the
first three of the above-named muscles the exterior muscles of
the larynx; the three others he comprehends under the name of
thyro-arytenoid or vocal muscle, which divides into three slips
in the interior of the larynx. This, however, as well as the
description of the character and action of the different muscles,
belongs to the department of science. What I have already stated
seems to me to be sufficient for an understanding of the action
of these organs in the production of sound in the different
registers. The reader is referred to any good manual of anatomy
for a full description of the muscles, ligaments, nerves, vessels
and membranes.