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The nerve supply is the anterior branch of the inferior laryngeal nerve.
The m. arytenoideus transversus is a thick, oblong, unpaired muscle which lies in the dorsal wall of the larynx and bridges across the interval between the two arytenoid cartilages. The ventral surface of the muscle is in contact with the dorsal concave surfaces of the arytenoid cartilages, and between them with the mucous membrane of the larynx. Its dorsal surface is partly concealed by the arytenoidei obliqui and by the submucous tissue of the pharynx. The inferior border extends to the lamina of the cricoid cartilage, and its upper border does not quite reach the apices of the arytenoid cartilages.
The attachments of the muscle are, on both sides, to the dorsal surface of the processus muscularis and the lateral edge of the arytenoid cartilages. All the fibres run in a frontal (coronal) direction, and some turn round the arytenoid cartilage to become continuous with the thyreo-arytenoideus. The arytenoideus transversus and the thyreo-arytenoid muscles form, together, a sphincter of the glottis
By its action the arytenoideus transversus approximates the arytenoid cartilages, thereby tending to close the pars intercartilaginea of the rima glottidis. Its assistance in the sphincter action of the thyreo-arytenoideus has already been pointed out.
The muscle is innervated by the posterior or dorsal rami of the inferior laryngeal nerve of both sides.
The mm. arytenoidei obliqui are a pair of muscles which lie in the dorsal wall of the larynx, immediately dorsal to the arytenoideus transversus and ventral to the submucous tissue of the pharynx.
Each muscle consists of a bundle of muscular fibres which arise from the dorsal aspect of the processus muscularis of the corresponding arytenoid cartilage. From their origins the two fleshy slips proceed upwards and medially, and cross each other in the median plane like the two limbs of the letter X. Reaching the apex of the arytenoid cartilage of the opposite side, many, but not all, of the fibres are inserted there, but others receiving a fresh attachment arise from the apex of the arytenoid cartilage as the m. aryepiglotticus, and extend ventrally and upwards in a series of arches within the aryepiglottic fold to terminate in the thyreo-epiglottic ligament and the lateral margin of the epiglottic cartilage; and as the muscle approaches the latter structure its fibres are joined by the fibres of the thyreo-epiglotticus. With its superior border are also commingled some fibres from the m. stylo-pharyngeus.
Action. The arytenoideus obliquus and aryepiglotticus combined, act as a rudimentary sphincter muscle for the aditus and the vestibulum laryngis, that is for the superior aperture of the larynx, inasmuch as they extend from the base of one arytenoid cartilage to the apex of the arytenoid cartilage of the opposite side. and then on to the epiglottis within the ary-epiglottic fold.
The two muscular slips are innervated by the corresponding anterior rami of the inferior laryngeal nerves.
The mm. cricoarytenoidei posteriores are a pair of triangular muscles, each of which lies on the dorsal surface of the lamina of the cricoid cartilage, under cover of the tela submucosa of the pharynx. Each arises, by a broad origin, from the medial and inferior part of the depression on the dorsal surface of the lamina of the cricoid cartilage at the side of the median ridge; from that origin its fibre converge upwards and laterally to be inserted into the dorsal surface and apex of the processus muscularis of the corresponding arytenoid cartilage. I their course from origin to insertion the muscular fibres display very different degrees of obliquity. The most superior fibres are short and nearly horizontal; the intermediate fibres are the longest and are very oblique; whilst the most inferior fibres are almost vertical in their direction.
By its action the crico-arytenoidei posteriores draw the muscular processe of the arytenoid cartilages medially and dorsally, swing the vocal processes and the vocal folds laterally, and thereby open the rima glottidis.
The muscle is innervated by the posterior ramus of the inferior laryngea
The mm. thyreoepiglottici are a pair of thin, oblong, very variable muscles
which lie in the side walls of the larynx. Each is bounded below by the thyreo - arytenoideus, medially by the thyreo - epiglottic ligament and the
appendix ventriculi laryngis, and laterally by the lamina of the thyreoid cartilage. It constitutes what was formerly described as the uppermost fibres of the thyreo-arytenoideus externus muscle.
Each thyreo-epiglotticus arises from the medial surface of the lamina of the thyreoid cartilage, immediately above the origin of the thyreo-arytenoideus. From this origin the fibres run in arches, upwards and dorsally, to be inserted partly into the margin of the aryepiglottic fold, and partly into the lateral margin of the epiglottis, being intermingled with the fibres of the aryepiglotticus.
By its action the thyreo-epiglotticus widens the aditus and the vestibulum laryngis. Its innervation is derived from the ventral ramus of the inferior laryngeal nerve.
The mm. cricothyreoidei are a pair of quadrangular muscles, broader and
-Ring of trachea
Cut surface of wall of vestibule of larynx Epiglottic tubercle Ventricular foldVentricle of larynx Vocal fold
M. vocalis M. thyreo-.. arytenoideus
FIG. 856.-FRONTAL SECTION OF THE LARYNX, SHOWING MUSCLES.
FIG. 855. THE CRICO-THYREOID MUSCLE OF THE RIGHT SIDE.
thicker above than below. They lie on the cricoid cartilage and bridge over the crico-thyreoid interval, and are, therefore, the only intrinsic laryngeal muscles which are visible in an ordinary dissection of the neck. Each is covered laterally and in part by the thyreoid gland and the sternothyreoid and the sterno-hyoid muscles. Between the two muscles of opposite sides there is an intermediate triangular area left in which the crico-thyreoid ligament is visible.
Each cricothyreoideus arises from the lower border and lateral surface of the arch of the cricoid cartilage, and from this origin its fibres radiate dorsally and upwards to be inserted into the inferior border and medial surface of the lamina of the thyreoid cartilage, as far as its inferior cornu, and also into the inferior cornu itself. As a general rule each muscle is divided into two parts, viz., (1) a pars recta composed of those fibres which are inserted into the lamina of the thyreoid car
tilage; and (2) a pars obliqua formed of those fibres which are inserted into the inferior cornu. The muscle is closely associated with the inferior constrictor
muscle of the pharynx, and sometimes shows a certain amount of continuity with it.
The general action of the crico-thyreoideus is to render the vocal fold tens. as is more fully set forth in the paragraph dealing with the actions of the intrinsic laryngeal muscles as a whole.
The innervation is derived from the external ramus of the superior laryngeal
The Mm. Vocales (O.T. Internal Thyreo-arytenoid Muscles). The vocalis muscle of each side is a triangular, somewhat prismatic muscle, which forms with the thyreo-arytenoideus a common muscular mass separable only with difficulty into its two constituent portions. The m. vocalis lies within the vocal fold, closely applied to the lateral aspect of the ligamentum vocale, and receives its prismatic form from this adaptation. Of its three surfaces, the medial lies adjacent to the ligamentum vocale and the conus elasticus; the upper surface is bounded by the labium vocale and the entrance to the ventricle of the larynx; whilst the lateral surface is bounded by, and is in contact with, the thyreo-arytenoideus.
The m. vocalis arises from the inferior part of the angular depression between the two lamina of the thyreoid cartilage, and also from the corresponding vocal fold, whence the fibres run dorsally to be inserted into the lateral aspect of the vocal process and the depression on the ventro-lateral surface of the arytenoid cartilage. The greater thickness of the m. vocalis dorsally than ventrally is due to the fact that whilst all its fibres are attached dorsally to the arytenoid cartilage, only a certain proportion obtain attachment ventrally to the thyreoid cartilage. The remainder are attached at irregular intervals to the lateral margin of the vocal fold itself.
It follows that the action of the muscle is to draw the vocal process of the arytenoid cartilage ventrally, thereby relaxing the vocal fold and ligament. The innervation is derived from the anterior ramus of the inferior laryngeal
The m. ventricularis is composed of several bundles of fibres, visible under the microscope, which pass, in a vertical direction, from the lateral edge of the arytenoid cartilage to the lateral margin of the cartilage of the epiglottis There are also intermingled with it fibres from the thyreo-arytenoideus and aryepiglotticus.
Action of the Intrinsic Laryngeal Muscles.-By the action of the intrinsic laryngeal muscles the position and tension of the vocal folds are so influenced that, during the passage of air through the larynx, the tone and the pitch of the voice is determined. Tension of the vocal folds is produced by the contraction of the two crico-thyreoid muscles. The straight portions of the muscles pull the inferior border of the thyreoid cartilage downwards, whilst the oblique portions, through their insertion inte the inferior cornua, draw the thyreoid cartilage ventrally, thereby increasing the distance between the angle of the thyreoid cartilage and the vocal processes of the arytenoid cartilages. When the crico-thyreoid muscles cease to contract, the relaxation of the cords is brought about by the elasticity of the ligaments. The thyreo-arytenoid muscles must be regarded as antagonistic to the crico-thyreoid muscles. When they contract they approximate the angle of the thyreoid cartilage to the arytenoid cartilages, and still further relax the vocal folds; and when they cease to act the elasticity of the ligaments of the larynx again restores the state of equilibrium. They also act as constrictors of the supraglottic region of the larynx. The vocales muscles, by the attachments of their fibres into the vocal folds, may tighten portions of these folds, but their main action is relaxation of the vocal folds and ligaments.
The width of the rima glottidis is regulated by the arytenoideus transversus which draws together the two arytenoid cartilages, and this may be done so effectually that the medial surfaces of these cartilages come into contact; the pars intercartilaginea of the rima glottidis is thus completely closed. The crico-arytenoidei, laterales and posteriores, also modify the width of the rima glottidis. When they act together they assist the arytenoideus transversus in closing the glottis, but when they act independently they are antagonistic muscles. Thus the crico-arytenoidei posteriores draw the muscular processes of the arytenoid cartilages dorsally and medially, and swing the vocal processes and the vocal folds laterally, and thereby open the rima. The
lateral crico-arytenoid muscles act in exactly the opposite manner. By drawing the muscular processes of the arytenoid cartilages ventrally and medially, they approximate the vocal processes and close the rima glottidis. The actions of the other muscles have been sufficiently described already.
Closure of the Larynx during Deglutition.-The muscles of the larynx have, however, another function to perform besides vocalisation and regulating the amount of air passing to and fro through the glottis. During deglutition it is requisite that the communication between the pharynx and larynx should be closed, to prevent the fluid or solid parts of the food entering the respiratory passages. In the process of closing the laryngeal entrance the epiglottis stands erect, whilst the dorsal wall formed by the arytenoids is carried ventrally, the arytenoid cartilages are closely approximated, glide ventrally, and are then inclined towards the epiglottis. The result of this is that the laryngeal opening is converted into a T-shaped fissure. The median limb of the T is formed by the interval between the closely applied arytenoid cartilages, whilst the cross limb, which lies ventrally, is bounded ventrally (anteriorly) by the epiglottis and dorsally by the aryepiglottic folds. The apices of the arytenoid cartilages, with the corniculate cartilages (Santorini), are pressed against the tubercle of the epiglottis, whilst the lateral margins of the epiglottis are pulled dorsally so as to make the transverse limb of the fissure distinctly concave in a dorsal direction. The muscles chiefly concerned in producing these movements are the thyreo-arytenoid and the transverse arytenoid muscles. These form a true sphincter vestibuli. The thyreo-epiglottic and aryepiglottic muscles also come into play. They pull upon the epiglottis so as to produce tight application of its tubercle to the arytenoid cartilages and the corniculate cartilages (Santorini), and they also curve its margins dorsally so as to increase its dorsal concavity.
Vessels and Nerves of the Larynx.-Two branches of the vagus nerve, viz., the superior laryngeal and the recurrent (laryngeal) nerves, supply the larynx. The superior laryngeal divides into the internal and external laryngeal branches. The external laryngeal nerve supplies the crico-thyreoid muscle; whilst the internal laryngeal nerve enters the larynx, by piercing the lateral part of the hyothyreoid membrane, to supply the laryngeal mucous membrane. The recurrent nerve reaches the larynx from the thoracic direction, and, by its terminal inferior laryngeal branch, supplies all the intrinsic laryngeal muscles, with the exception of the crico-thyreoid.
The superior laryngeal artery, a branch of the superior thyreoid, accompanies the internal laryngeal nerve; whilst the inferior laryngeal artery, which springs from the inferior thyreoid, accompanies the inferior laryngeal nerve. These two vessels ramify in the laryngeal wall and supply the mucous membrane, the glands, and muscles.
Growth-Alteration and Sexual Differences in the Larynx.-A considerable amount of variation may be noticed in the size of the larynx in different individuals. This is quite independent of stature, and explains to a great extent the difference in the pitch of the voice in different persons. But quite apart from these individual variations, there is a marked sexual difference in the size of the larynx. The male larynx is not only absolutely, but also relatively, larger than the female larynx in all its diameters, but more particularly in the ventro-dorsal diameter; and to a large extent the increase in that direction is produced by the strong development of the prominentia laryngea in the male. The greater ventro-dorsal diameter of the male larynx necessarily implies a greater length. of the vocal folds and a lower or deeper tone of the voice in the male than in the female. In a newly born child the larynx, in comparison with the rest of the body, is somewhat large (C. L. Merker), and it continues to grow slowly and uniformly up to the sixth year of childhood. At that period there is a cessation of growth until puberty is reached, and then a stage of active growth supervenes. Up to that time the larynx in both sexes is similar in its dimensions, and although the growth which now occurs affects both the male and the female larynx, it is much more rapid and much more accentuated in the male than in the female. As a result the voice of the male "breaks" and assumes its deep tone.
It is interesting to note that the growth activity of the larynx, at puberty, is intimately connected with the development of the sexual organs. In a male subject who has been castrated, when young, the larynx attains a size which exceeds that of the female only to a small degree, and the high pitch of the voice is retained.
Appearance of the Interior of the Larynx when examined by the Laryngoscope.
When the cavity of the larynx is illuminated and examined by laryngoscopic mirrors, the parts which surround the superior aperture of the larynx, as well as the interior of the organ, come into view. Not only this, but when the vocal folds are widely separated it is possible to inspect the interior of the trachea as far as its bifurcation.
In such an examination the arched upper border of the epiglottis is a conspicuous object, whilst, dorsal to that, the bulging on the ventral wall of the vestibule, formed by the tubercle of the epiglottis, may also be a feature of the picture. The median glosso-epiglottic fol with the glosso-epiglottic vallecula on either side of it, can also be inspected in the interva between the epiglottis and the base of the tongue. The sharp aryepiglottic folds are clearly visible, and in the dorsal portion of each can be seen the two prominent tubercle which. are formed by the enclosed cuneiform and corniculate cartilages. Dorsal to those tubercles is the dorsal wall of the pharynx, whilst to their lateral side the deep piriform Median glosso-epiglottic fold Dorsum of tongue
FIG. 857.-CAVITY OF THE LARYNX, as seen by means of the laryngoscope.
recess may be seen. In the interior of the larynx the ventricular and the vocal folds are easily recognised, and the interval between the two, or, in other words, the entrance into the laryngea ventricle, appears as a dark line on the lateral wall of the larynx. The ventricular folds are red and fleshy-looking; the vocal folds during phonation are tightly stretched and pearly whitethe white colour being usually more apparent in the female than in the male. The outline and yellowish tinge of the vocal process at its attachment to the vocal fold, and the outline of the ventral part of the base of the arytenoid cartilage to a slight extent as well, can be made out in a successful laryngoscopic examination. The vocal folds during ordinary inspiration are seldom at rest, and with the laryngoscope their movements may be studied. It should be borne in mind that the picture afforded by the laryngoscope does not give a true idea of the level at which the different parts lie. The cavity appears greatly shortened, and its depth diminished.
The trachea or windpipe is a wide tube which is kept permanently patent by a series of bent cartilaginous bars embedded in its wall. These bars are deficient dorsally, and consequently the tube is not completely cylindrical: its dorsal wall is flattened. The trachea begins at the inferior border of the cricoid cartilage, opposite the inferior margin of the sixth cervical vertebra. From that level it extends, through the neck, into the superior mediastinum of the thorax, and it ends, at the level of the superior border of the fifth thoracic vertebra, by dividing into the right and left bronchi. The length of the trachea in the male is from four to four and a half inches, and in the female from three and a half to four inches, but even in the same individual it varies considerably in length with the movements of the head and neck.
The inferior end of the trachea is fixed in position. This is a necessary provision to prevent dragging on the roots of the lung during movements of the head and neck. The remainder of the tube is surrounded by a quantity of loose areolar tissue, and possesses a considerable amount of mobility. Further, its wall is highly elastic, and thus when the head is thrown back the tube elongates through stretching, and when the chin is depressed its length is diminished by the recoil of its wall.
The trachea does not present an absolutely uniform calibre throughout its whole length. About its middle it exhibits a slight expansion or dilatation, and from that the calibre diminishes towards both extremities. Close to the bifurcation it is again slightly expanded (Braune and Stahel).