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the arytenoid cartilages. These small nodules of cartilage raise the dorsal part of the ary-epiglottic fold in the form of two rounded eminences, termed respectively the tuberculum cuneiforme [Wrisbergi] and the tuberculum corniculatum [Santorini].
On each side of the laryngeal opening there is, in the pharynx, a small recess, directed downwards, which presents a wide entrance, but rapidly narrows towards. the bottom. It is termed the recessus piriformis, and is of importance to the surgeon, because foreign bodies introduced into the pharynx are liable to be caught in this little pocket. On the medial side the recessus piriformis is bounded by the arytenoid cartilage and the ary-epiglottic fold, whilst on the lateral side it is limited by the inner surface of the laminae of the thyreoid cartilage, clothed with the pharyngeal mucous membrane.
Vestibulum Laryngis. The vestibule of the larynx is the uppermost compartment of the cavity of the larynx. It extends from the laryngeal aperture to the ventricular folds. In its inferior part it exhibits a marked lateral compression. Its width, therefore, diminishes in the vertical direction, whilst, owing to the obliquity of the laryngeal aperture, its depth rapidly diminishes ventrodorsally. Ventrally it is bounded by the dorsal surface of the epiglottis, clothed with mucous membrane. This wall passes obliquely from its superior end in an inferior ventral direction, and becomes narrower as it approaches the ventral or anterior ends of the ventricular folds. The superior part of the dorsal surface of the epiglottis is convex, owing to the manner in which the upper margin is curved ventrally towards the tongue; below the convexity there is a slight concavity, and still lower a marked bulging or convexity, over the superior part of the thyreo-epiglottic ligament. This swelling is called the tuberculum epiglotticum, and it forms a conspicuous object in laryngoscopic examination of the larynx. Each lateral wall of the vestibule of the larynx is formed by the medial surface of the corresponding aryepiglottic fold. For the most part it is smooth and slightly concave, and it diminishes considerably in vertical depth as it passes dorsally. FIG. 850.-FRONTAL SECTION THROUGH THE In its dorsal part the mucous membrane stands out in two elongated vertical elevations, placed one dorsal to the other (Fig. 849, p. 1068). The more ventral elevation is formed by the subjacent cuneiform cartilage with the mass of glands associated with it; the more dorsal elevation is produced by the upper part of the arytenoid cartilage and the corniculate cartilage (Santorini). A shallow groove (philtrum ventriculi of Merkel) passes downwards between these rounded elevations, and terminates below by running into the interval between the ventricular and vocal folds. The ventral elevation ends below in the dorsal extremity of the ventricular fold; the arytenoid or dorsal elevation, in its inferior part, bends round the dorsal end of the ventricle of the larynx and becomes lost in the vocal fold. The dorsal wall of the laryngeal vestibule is narrow, and corresponds to the interval between the upper parts of the two arytenoid cartilages. Its width, to a large extent, depends on the position of those cartilages, and when they are placed near each other the mucous membrane which covers the dorsal wall is thrown into longitudinal folds.
LARYNX TO SHOW ITS COMPARTMENTS.
The middle compartment of the larynx is much the smallest of the three. It is bounded above by the ventricular fold and below by the vocal folds, whilst it communicates between those folds with the vestibule on the one hand and the inferior compartment on the other.
fold Tubercle of epiglottis
The ventricular folds (O.T. false vocal cords) are two prominent folds of mucous membrane which extend ventro-dorsally on the lateral walls of the laryngeal cavity. Ventrally they reach the angle between the two laminæ of the thyreoid cartilage, but dorsally they do not extend so far as the dorsal wall of the larynx. They come to an end at the inferior extremity of the elongated swelling produced by the cuneiform cartilage. The ventricular fold is soft and somewhat flaccid, and presents a free border which is slightly arched the concavity looking downwards. Within the fold of mucous membrane which forms this fold are contained: (1) the feeble ventricular ligament; (2) numerous glands which are chiefly aggregated in its middle part; and (3) a few muscle fibres.
The interval between the ventricular folds is sometimes termed the rima vestibuli (O.T. false glottis), and is considerably wider than the interval between the two vocal folds, which is called the rima glottidis. It follows, from this, that when the cavity of the larynx is examined from above the four folds are distinctly visible, but when examined from below the vocal folds alone can be seen.
The vocal folds (O.T. true vocal cords), placed below the ventricular folds, extend from the angle between the laminæ of the thyreoid cartilage ventrally, to the vocal processes of the arytenoid cartilages dorsally. The vocal fold is sharp and prominent, and the mucous membrane which is stretched over it is very thin and firmly bound down to the subjacent ligament. In colour it is pale, almost pearly white, whilst. dorsally, the point of the processus vocalis of the arytenoid, which stands out clearly in relief, presents a yellowish tinge. In cross-section the vocal fold is prismatic in form, and its free border looks upwards as well as medially.
The vocal folds are the agents by means of which the voice is produced. The ventricular folds are of little importance in this respect; indeed, they can in great part be destroyed and no appreciable difference in the voice result.
Rima Glottidis.-This name is applied to the elongated fissure by means of which the middle compartment of the larynx communicates with the lower compartment. It is placed somewhat below the middle of the laryngeal cavity, of which it constitutes the narrowest part. Ventrally it corresponds to the interval between the vocal folds; dorsally it corre- A. During ordinary easy breathing. B. Widely opened. sponds to the interval between the bases
FIG. 852.-DIAGRAM OF RIMA GLOTTIDIS.
FIG. 851.-SECTION THROUGH LARYNX IN THE
OF THE RIGHT HALF.
Vocal process of arytenoid cartilage
and vocal processes of the arytenoid cartilages. It is composed, therefore, of two distinct parts: (1) a narrow ventral portion, between the vocal folds, involving
more than half of its length, and called the pars intermembranacea of the rima glottidis; (2) a broader, shorter portion, between the arytenoid cartilages, and termed the pars intercartilaginea. By changes in the position of the arytenoid cartilages the form of the rima glottidis undergoes constant alterations. In ordinary easy breathing it is somewhat lanceolate in outline. The pars intermembranacea presents, under these conditions, the form of an elongated triangle the base of which is directed dorsally and corresponds to an imaginary line drawn between the points of the vocal processes of the arytenoid cartilages, whilst the pars intercartilaginea is somewhat quadrangular. When the glottis is opened widely the broadest part of the fissure is at the extremities of the vocal processes of the arytenoids, and there each side of the rima glottidis presents a marked angle. The two vocal folds, on the other hand, may be approximated to each other so closely, as in singing a high note, that the pars intermembranacea is reduced to a linear chink.
The length of the rima glottidis differs very considerably in the two sexes, and upon this depends the different character of the voice in the male and female. According to Moura, the following are the average measurements in the quiescent condition of the rima :
Male-Length of entire rima glottidis, 23 mm.
pars intermembranacea, 15.5 mm.
Female-Length of entire rima glottidis, 17 mm.
By stretching the vocal folds, however, the length of the rima glottidis in the male may be increased to 275 mm., and in the female to 20 mm.
The position of the rima glottidis may be indicated on the surface by marking a point on the middle line of the neck 8.5 mm. below the thyreoid notch in the male and 65 mm. in the female. This is the average position (Taguchi).
Ventriculus Laryngis (Morgagnii).—The lateral wall of the larynx, in the interval between the ventricular and the vocal folds, exhibits a marked pocketlike depression or recess called the ventricle of the larynx. The ventricle passes upwards, so as to undermine somewhat the ventricular fold, and its mouth is somewhat narrower than its cavity. Ventrally it reaches to the angle between the lamina of the thyreoid cartilage, whilst dorsally it ends at the ventral border of the arytenoid cartilage.
Under cover of the ventral part of the ventricular fold a small slit-like aperture may be detected; this leads upwards from the laryngeal ventricle into a small diverticulum of mucous membrane, termed the appendix ventriculi laryngis, which passes upwards, between the ventricular fold and the lamina of the thyreoid cartilage. The laryngeal appendix is of variable extent, but as a rule it ends blindly at the level of the upper border of the thyreoid cartilage.
Sometimes the appendix ventriculi laryngis extends much higher up, and may even reach the dorsal part of the great cornu of the hyoid bone. This is of interest when considered in connexion with the extensive laryngeal ponches of the anthropoid apes.
The lowest compartment of the cavity of the larynx leads caudally into the trachea. Above it is narrow and compressed laterally, but it gradually widens out until it becomes circular, in correspondence with the trachea, with which it is continuous. It is bounded by the sloping medial surfaces of the conus elasticus (O.T. cricothyreoid membrane) and by the medial aspect of the cricoid cartilage-both covered with smooth mucous membrane. In the operation of laryngotomy the opening is made through the crico-thyreoid ligament in the ventral wall of this compartment.
Tunica Mucosa Laryngis. The mucous membrane which lines the larynx is continuous above with the lining of the pharynx, and below with the mucous membrane of the trachea. Over the dorsal surface of the epiglottis it is closely adherent, but elsewhere, above the level of the vocal folds, it is loosely attached by submucous tissue which extends into the ary-epiglottic folds. As it passes over the vocal folds the mucous membrane is very thin, and is tightly bound down.
It is important to bear these facts in mind, because, in certain inflammatory conditions, the lax submucous tissue in the upper part of the larynx is liable to become infiltrated with fluid,
producing what is known as oedema glottidis. This may proceed so far as to cause occlusion of the upper part of the cavity. The close adhesion of the mucous membrane to the vocal folds, however, prevents the oedema extending beyond the level of the rima glottidis, and the surgeon is thus able to relieve the patient by making an opening through the ventral part of the conus elasticus into the cavity of the larynx.
Above the level of the rima glottidis the laryngeal mucous membrane is extremely sensitive, and when touched by a foreign body there is an immediate response in the shape of an explosive cough. In the lower compartment of the larynx the mucous membrane is lined with columnar ciliated epithelium. Over the vocal folds this is replaced by squamous epithelium. In the ventricle of the larynx and in the inferior part of the vestibule of the larynx the columnar ciliated epithelium again reappears. The upper part of the epiglottis and the upper parts of the lateral walls of the vestibule are covered with squamous epithelium similar to that present in the mouth and pharynx.
The mucous membrane of the larynx has a plentiful supply of acinous glands, and in only one place, viz., over the surface of the vocal folds, are these completely absent. For the most part the glands are aggregated in groups. The following are the localities in which these groups are especially noticeable: (1) On the dorsal surface of the epiglottis, many of the glands piercing the cartilage; (2) around the cuneiform cartilage, where they are chiefly responsible for the elongated elevation seen in this part of the wall of the vestibule; (3) in the ventricular folds and over the wall of the laryngeal vestibule and the appendix ventriculi laryngis.
Of the several muscles attached to the cartilages of the larynx all do not physiologically belong to the larynx, as, for example, the inferior constrictor muscles of the pharynx, which, though attached to both cricoid and thyreoid cartilages, belong to the muscles of the pharynx, as do also the stylo-pharyngeus and palato-pharyngeus muscles inserted in part into the thyreoid cartilage.
The true physiological muscles of the larynx may be divided into two great groups, extrinsic and intrinsic. The extrinsic laryngeal muscles comprise all muscles passing to the os hyoideum, which is physiologically a part of the laryngeal apparatus, as well as the m. sterno-thyreoideus. They have already been described in the section on muscles.
The intrinsic laryngeal muscles are nineteen in number, nine paired and one unpaired. They may be roughly classified physiologically as follows:
A. Constrictor muscles of the larynx, including the adductors of the vocal folds—
Mm. thyreoarytenoidei. Paired.
M. arytenoideus transversus. Unpaired.
Mm. arytenoidei obliqui. Paired.
Mm. aryepiglottici. Paired.
B. Dilator muscles of the larynx, including the abductors of the vocal folds
Mm. cricoarytenoidei posteriores.
Mm. thyreoepiglottici. Paired.
C. Muscles modifying the tension of the vocal cords-
Mm. cricothyreoidei. Paired.
Mm. vocales. Paired.
Mm. ventriculares. Paired.
Mm. thyreoarytenoidei (also constrictors).
The mm. cricoarytenoidei laterales are a pair of triangular muscles, each of which lies in the lateral wall of the larynx upon the conus elasticus and concealed by the lamina of the thyreoid cartilage, the thyreoid gland, and the infrahyoid muscles.
Each muscle arises from the upper border and the lateral surface of the arch of the cricoid cartilage as far dorsally as the facet which supports the base of the arytenoid cartilage, and also from the lateral part of the conus elasticus.
From this origin the muscular fibres run dorsally and upwards, and converge to be inserted into the ventral surface of the processus muscularis of the arytenoid cartilage. The muscle is not infrequently inseparable from the (external) thyreo-arytenoid muscle.
By its action the lateral crico-arytænoid muscle draws the processus muscularis of the arytenoid cartilage ventrally and downwards, thus turning the processus vocalis of the same cartilage medially, and tending thereby to stretch the vocal fold and to approximate it to its fellow of the opposite side, thus assisting in closure of the rima glottidis. Its nerve supply is the anterior ventral branch of the inferior 7 laryngeal nerve.
M. thyreoarytenoideus-M. crico-ary
M. cricoarytenoideus posterior Conus elasticus
The Mm. Thyreoarytenoidei (O.T. tenoideus lateralis Externus). Thyreoarytenoideus Each thyreo- arytenoid muscle is a thin, quadrangular muscle, which is only separable from the corresponding m. vocalis, with which it forms a common mass, by artificial means.
It lies in the lateral wall of the larynx, immediately to the medial side of the lamina of the thyreoid cartilage, and lateral to the appendix ventriculi laryngis, the m. vocalis, and the conus elasticus; its inferior border is in contact with the lateral crico-arytenoid
Epiglottic tubercle Superior cornu of thyreoidcartilage Ary-epiglottic Inuscle
arytenoid muscle Oblique arytenoid muscle
FIG. 854.-DISSECTION OF THE MUSCLES ON THE
Muscular process of arytæ noid cartilage
FIG. 853.--DISSECTION OF THE MUSCLES OF THE
muscle, whilst its superior border extends farther upwards than the vocal fold, and is in contact with the inferior border of the thyreo-epiglotticus.
It arises from the inferior half of the medial surface of the lamina of the thyreoid cartilage, close to its ventral angle, and also from the lateral part of the conus elasticus. The muscular fibres pass dorsally and upwards to be inserted into the lateral border and muscular process of the arytenoid cartilage; some of the fibres, however, turn round this cartilage and become continuous with the arytenoideus transversus. The upper fibres of the thyreo-arytenoideus vary very greatly in their development and arrangement.
By its action the muscle rotates the arytenoid cartilage and draws it ventrally in such a way that its vocal process is carried ventrally and medially and the vocal fold is rendered somewhat flaccid. The muscle thus antagonises the crico-thyreoideus. The main action of the muscle must, however, be that of a constrictor of the supraglottic region. of the larynx.