The larynx is a sound-giving organ belonging to that class of wind instruments called reed instruments, although it differs in various respects from all artificial arrangements of the kind. The sound or tone-generating apparatus of the larynx consists of tense, elastic membranes, the so-called chordÆ vocales, which are enclosed in a sounding case composed of movable cartilaginous plates, and may be stretched by a certain apparatus of muscles in very different and exactly measurable degrees. They are made to vibrate audibly by a current of air impelled with various degrees of force and at will by the lungs in expiration through the narrow chink (glottis) formed by the fine edges of the chords. Thus the lungs correspond to the bellows of the organ; the trachea, at the top of which the vocal instrument is placed, answers to the conduit (Windrohr), and the cavity of the throat in front of the instrument with its two avenues, the mouth and the nostrils, to the resonance pipe (Ansatzrohr).
THE LUNGS
The lungs are two cellular, sponge-like elastic organs, largely made up of little cavities of conical shape, which, in the regular alternations of two opposite respiratory movements of air, are at one time expanded, and then again compressed. The two lungs are not of equal size; the right lung is one-tenth larger in volume than the left.
THE TRACHEA, OR WINDPIPE,
Through which the air of the lungs enters and passes out, consists of from sixteen to twenty-six cartilaginous rings, posteriorly incomplete, lying horizontally one above the other.
These rings are connected by a membrane covering them externally and internally. As they enter the cavity of the chest, they divide into two branches, likewise composed of rings, one entering the right, the other the left lung. Before they join the lungs they divide again into several smaller branches, which again subdivide fork-like in the lungs, and terminate in numberless little grape-like clusters of hollow vesicles. The diameter of the trachea in adults is from one-half to three-fourths of an inch when at rest.
THE LARYNX
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
- Thyroid cartilage.
- Cricoid cartilage.
The cartilages in the interior are:
- The Arytenoid cartilages.
- Cartilages of Wrisberg.
- Cartilages of Santorini.
- 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 oesophagus, 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 oesophagus, 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 oesophagus 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:
- The posterior crico-arytenoid.
- The lateral crico-arytenoid.
- The crico-arytenoid.
- The thyro-arytenoid.
- The arytenoid.
- 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.
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THE END.