THE LARYNX3
The Rima Glottidis is the narrow triangular fissure or chink between the infejrior or true chordae vocales. Its length, in the male, measures rather less than an inch, its breadth varying at its widest part from a third to half an inch. In the female, these measurements are less by two or three lines. The form of the aperture varies; in ordinary respiration it is a narrow interval, being somewhat enlarged and rounded behind; but when dilated, it is triangular in form, narrow in front and broad behind.
The Superior or False Vocal Cords, so called because they are not concerned in the production of the voice, are two thick folds of mucous membrane, enclosing a delicate narrow fibrous band, the
superior thyro-arytenoid ligament. This ligament consists of a thin band of elastic tissue, attached in front to the receding angle of the thyroid cartilage below the epiglottis, and behind to the tubercle on the anterior and inner surface of the arytenoid cartilage. The lower border of this ligament, enclosed in mucous membrane, forms a free crescentic margin, which constitutes the upper boundary of the ventricle of the larynx.
The Inferior or True Vocal Cords, so called from their being concerned in the production of sound, are two thick and strong fibrous bands (inferior thyro-arytenoid ligaments), covered externally by a thin and delicate mucous membrane. Each ligament consists of a compact band of parallel fibres of yellow elastic tissue, attached in front to the centre of the depression between the two alae of the thyroid cartilage, and behind to the anterior angle of the base of the arytenoid. Its inferior border is continuous with the thin lateral part of the crico-thyroid membrane. Its superior border forms the lower boundary of the ventricle of the larynx. Externally, the Thyro-arytenoideus muscle lies parallel with it. It is covered internally by inucoua membrane, which is extremely thin, and closely adherent to its surface.
The Ventricle of the Larynx is an oblong fossa, situated between the superior and inferior vocal cords on each side, and extending nearly their entire length. This fossa is bounded above by the free crescentic edge of the superior vocal cord; below, by the straight margin of the true vocal cord; externally, by the corresponding Thyro-arytenoideus muscle. The anterior part of the ventricle leads up by a narrow opening into a caecal pouch of mucous membrane of variable size, called the laryngeal pouch.
The Sacculus Laryngis, or laryngeal pouch, is a membranous sac, placed between the superior vocal cord and the inner surface of the thyroid cartilage, occasionally extending as far as its upper border; it is conical in form, and curved slightly backwards, resembling in form a Phrygian cap. On the surface of its mucous membrane are the openings of sixty or seventy small follicular glands, which are lodged in the submucous areolar tissue. This sac is enclosed in a fibrous capsule, continuous below with the superior thyro-arytenoid ligament; its laryngeal surface is covered by the Aryteno-epiglottideus inferior muscle (Compressor sacculi laryngis, Hilton); whilst its exterior is covered by the Thyro-epiglottideus muscle. These muscles compress the sacculus laryngis, and discharge the secretion it contains upon the chordae vocales, the surface of which it is intended to lubricate.
muscles. The intrinsic muscles of the larynx are eight in number; five of which are the muscles of the chordae vocales and rima glottidis; three are connected with the epiglottis.
The five muscles of the chorda; vocales and rima glottidis are the
The Crico-thyroid is triangular in form and situated at the fore part and side of the cricoid cartilage. It arises from the front and lateral part of the cricoid cartilage; its fibres diverge, passing obliquely upwards and outwards, to be inserted into the lower and inner borders of the thyroid cartilage; from near the median line in front, as far back as the inferior cornu.
The inner borders of these two muscles are separated in the middle line by a triangular interval, occupied by the crico-thyroid membrane.
The Crico-arytaenoideus posticus arises from the broad depression occupying each lateral half of the posterior surface of the cricoid cartilage; its fibres pass upwards and outwards, and converge to be inserted into the outer angle of the base of the arytenoid cartilage. The upper fibres are nearly horizontal, the middle oblique, and the lower almost vertical.
The Crico-arytaenoideus lateralis is smaller than the preceding, and of an oblong form. It arises from the upper border of the side of the cricoid cartilage, and passing obliquely upwards and backwards, is inserted into the outer angle of the base of the arytenoid cartilage, in front of the preceding muscle.
The Thyro-arytanoideus is a broad flat muscle, which lies parallel with the outer side of the true vocal cord. It arises in front from the lower half of the receding angle of the thyroid cartilage, and from the crico-thyroid ligament. Its fibres pass horizontally backwards and outwards, to be inserted into the base and anterior and outer surface of the arytenoid cartilage. This muscle consists of two fasciculi. The inferior, the thickest, is inserted into the anterior angle of the base of the arytenoid cartilage, and into the adjacent portion of its anterior surface; it lies parallel with the true vocal cord, to which it is occasionally adherent. The
superior fasciculus, the thinnest, is inserted into the anterior surface and outer border of the arytenoid, above the preceding fibres; it lies on the outer side of the sacculus laryngis, immediately beneath its mucous lining.
The Arytaenoideus is a single muscle, filling up the posterior concave surface of the arytenoid cartilages. It arises from the posterior surface and outer border of one arytenoid cartilage, and is inserted into the corresponding parts of the opposite cartilage. It consists of three planes of fibres, two oblique and one transverse.
'ine oblique fibres, the most superficial, form two fasciculi, which pass from the base of one cartilage to the apex of the opposite one. The transverse fibres, the deepest and most numerous, pass transversely across between the two cartilages; hence the Arytenoideus was formerly considered as several muscles, under the names of transversi and obliqui. A few of the oblique fibres are occasionally continued round the outer margin of the cartilage, and blend with the Thyro-arytenoid or the Aryteno-epiglottidean muscle. The muscles of the epiglottis are the
Thyro-epiglottideus. Arytaesno-epiglottideus superior. A ry tanio-epiglottideus inferior.
The Thyro-epiglottideus is a delicate fasciculus, which arises from the inner surface of the thyroid cartilage, just external to the origin of the Thyro-arytenoid muscle, and spreading out upon the outer surface of the sacculus laryngis, some of its fibres are lost in the aryteno-epiglottidean fold, whilst others are continued forwards to the margin of the epiglottis (denressor eniiilnttiilis\.
The Arytieno-epiglottideus superior consists of a few delicate, muscular fasciculi, which arise from the apex of the arytenoid cartilage, and become lost in the fold of mucous membrane extending between the arytenoid carl ihi.gc and side of the epiglottis (aryteno-epiglottidean folds).
The Arytceno-epiglottideus inferior (Compressor sacculi luryngis, Hilton) arises from the arytenoid cartilage, just above the attachment of the superior vocal cord, and passing forwards and upwards, spreads out upon the inner and upper part of the sacculus laryngis, and is inserted, by a broad attachment, into the margin of the epiglottis. This muscle is separated from the preceding by an indistinct areolar interval.
Actions. In considering the action of the muscles of the larynx, they may be conveniently divided into two groups, viz.: I. Those which open and close the glottis. 2. Those which regulate the degree of tension of the vocal cords.
I. The muscles which open the glottis are the Crico-arytienoidei postici, and those which close it are the Aryhwioideus, the Crico-arytr.:noirtei latcrales, and the Thyro-arytrenoidci. 2. The muscles which regulate the tension of the vocal cords are the Crico-thyroidei, which tense and elongate them, and the Thyro-arytse-noiclei, which relax and shorten them. The Thyro-epiglottideus is a depressor of the epiglottis, and the Arytrcno-epiglottidei constrict the superior aperture of the larynx, compress the sacculus laryngis, and empty it of its contents.
The Crico-«rytaenoidei postici separate the chordae vocales, and consequently open the glottis, by rotating the base of the arytenoid cartilages outwards and backwards; so (hat their anterior angles, and the ligaments attached to them, become widely separated.
The Crico-arytaenoidei laterales close the glottis, by rotating the base of the arytenoid cartilages in the opposite direction to the last-named muscles, so as to approximate their anterior angles.
The Arytaenoideus muscle approximates the arytenoid cartilages, and thus closes the opening of the glottis.
The Crico-thyroid muscles effect the tension and elongation of the vocal cords.
The Thyro-arytaenoidei muscles approximate the anterior angles of the arytenoid cartilages, and thus constrict the glottis. According to Willis, they also draw the arytenoid cartilages, together with the part of the cricoid to which they are connected, forwards, and thus shorten and relax the vocal cords.
The Thyro-epiglottidei depress' the epiglottis, and assist in compressing the sacculus laryngia. The Arytaeno-epiglottideus superior, constricts the superior aperture of the larynx, when it is drawn upwards, during deglutition, and the opening closed by the epiglottis. The Arytaeno-epiglottideus inferior, together with some fibres of the Thyro-arytsenoidei, compress the sacculus laryngis.
The Mucous Membrane of the Larynx is continuous, above, with that lining the mouth and pharynx, and is prolonged through the trachea and bronchial tubes into the lungs. It lines both surfaces of the epiglottis, to which it is closely adherent, and forms the aryteno-epiglottidean folds, which encircle the superior aperture of the larynx. It lines the whole of the cavity of the larynx; forms, by its reduplication, the chief part of the superior, or false vocal cords; and from the ventricle is continued into the sacculus laryngis. It is then reflected over the true vocal cords, where it is thin, and very intimately adherent; covers the inner surface of the crico-thyroid membrane, and cricoid cartilage; and is ultimately continuous with the lining membrane of the trachea. It is covered with a columnar ciliated epithelium, below the superior vocal cord, but, above this point, the cilia; are found only in front, as high as the middle of the epiglottis. In the rest of its extent, the epithelium is of the squamous variety.
Glands. The mucous membrane of the larynx is furnished with numerous muciparous glands, the orifices of which are found in nearly every part: they are very numerous upon the epiglottis, being lodged in little pits in its substance: they are also found in large numbers along the posterior margin of the aryteno-epiglottidean fold, in front of the arytenoid cartilages, where they are termed the arytenoid glands. They exist also in large numbers upon the inner surface of the sacculus laryngis. None are found on the vocal cords.
The Arteries of the larynx are the laryngeal branches derived from the superior and inferior thyroid.
The Veins empty themselves into the superior, middle, and inferior thyroid veins.
The Lymphatics terminate in the deep cervical glands.
The Nerves are the superior laryngeal, and the inferior or recurrent laryngeal branches of the pneumogastric nerves, joined by filaments from the sympathetic. The superior laryngeal nerve supplies the mucous membrane of the larynx, and the Crico-thyroid muscle. The inferior laryngeal nerve supplies the remaining muscles. The Arytenoid muscle is supplied by both nerves.
