The crico-arytenoidei postici rotate the arytenoid cartilages outward, separating the vocal processes, and, acting in conjunction with the posterior fibres of the crico-arytenoidei laterales, draw the cartilages outward and downward.
In the cadaveric condition, which is one of relaxation of all the laryngeal muscles, the glottis is neither closed nor widely open; the epiglottis is erect against the dorsum of the tongue; the arytenoid cartilages are slightly separated, so that the glottic opening is a triangle with the base posteriorly, as in the act of inspiration, but the separation is much less than in the act of breathing. This condition is met with in paralysis affecting all the muscles of the organ.
The nerves of the larynx are derived from the pneumogastrics. The superior laryngeal is mainly a nerve of sensation for the parts above the edges of the vocal bands. There are some notable exceptions to this statement: a branch, external, descends to the crico-thyroid muscles and is motor in its function. Filaments from the superior laryngeal endowed with motor functions are also distributed to the folds extending from the arytenoids to the epiglottis; these are the ary-epiglottidean bands, and are concerned in the movements of the epiglottis. It is probable that the arytenoids are also in part supplied by the superior laryngeal; in other words, that both the superior and inferior laryngeal nerves are mixed, branches from the spinal accessory, as well as from the pneumogastric proper, entering to each of these nerves. Beclard1 states that the one, the spinal accessory, is a nerve of phonation; the other, the pneumogastric, is a nerve of respiration. The sensations of the mucous surfaces below the glottis depend upon filaments from the pneumogastrics returned along with the motor fibres from the spinal accessory. The two orders of fibres go to make up the recurrents. The relations of the recurrents themselves to the large vessels, as well as to the bronchial glands, are of importance. At the point of their origin they are in close relation with the aorta and right subclavian; they are also in close relation with the top of the lungs. Disease of these organs and structures, especially of the large blood-vessels, such as aneurism of the aorta or subclavian, disease of the glands, tumors, abscess, traumatism, etc., may modify or completely destroy the functions of the laryngeal nerves. In short, anything or any condition by which pressure may be made upon the pneumogastrics or recurrents may become a cause of nervous disturbance in the larynx. In addition to this general source of innervation, Elsberg2 describes a special centre of sensation for the throat in the medulla oblongata. He also describes three kinds of sensibility in the larynx—tactile, dolorous, and reflex. Rossbach3 details experiments from which he concludes that there are nerve-cells in the mucous membrane of the larynx which preside over the function of secretion. The larynx is endowed with at least two kinds of sensibility: the one tactile—when exalted it becomes painful; the other, reflex sensibility, is double. First, there is as a result of excitement a contraction of the subjacent muscle, and there follows closure of the glottis. This is seen in the application of irritants to the parts, such as solutions of nitrate of silver or other escharotics. There is no cough, but great difficulty of inspiration. Expiration is free and easy. There may follow some degree of pain for several hours. It will be seen that the phenomena are the same as those observed in the irritation of other mucous surfaces. The irritation is immediately translated into motion; this motion is probably reflex, but not necessarily through the centres, such as the brain or cord. The motion is of the subjacent muscles. Second, the mechanical irritation produced by the presence of a drop of water or a morsel of food in the larynx results in violent and explosive cough. The cough persists until the offending drop or body has been removed. This kind of sensibility calls into action distant muscles. There is no spasm of the adductors of the glottis, as in the case of the application of caustics. It is probable that the filaments of the nerves, the irritation of which gives rise to spasm, are distributed more generally than those which preside over reflex action at a distance and produce cough. The one set of functions are designed probably to protect the organ from the intrusion of foreign bodies; the other for their expulsion, as well as for the removal of the secretions of the parts or of matter brought up from below. The hypothesis of a third form of sensibility, as described by Elsberg—namely, the dolorous—seems hardly to be demanded for the larynx more than for all other mucous surfaces subject to pain. The nerve-cells of Rossbach in the mucous membrane may be peculiar to the larynx and trachea, as he claims, but further observations are required for the demonstration of this as a special histological fact distinguishing laryngeal from other mucous surfaces.
1 Dic. Eng. des Sci. med.
2 Int. Med. Cong., 1881.
3 Ibid.
PERVERSION OF SENSATION OF THE LARYNX.
There is some difficulty in grouping the derangements of the sensibility of the larynx, for the reason that in many cases the perversion of this function is only a symptom of some other disease of the organ. Probably in all cases the trouble is, in fact, an expression either of disturbance in the structures of the larynx, involving more than the sensory nerves, or it is the result of change in structure or function of neighboring or distant parts. Various attempts have been made to classify these disorders according to the kind of perversion and also according to the cause of the trouble. Elsberg, in a paper presented to the International Congress, London, 1881, p. 224. vol. iii., makes an attempt at a scientific classification based upon anatomico-physiological facts. That there is yet much to learn in regard to these facts, especially the physiological facts, will be admitted by every one at all familiar with the literature of the subject. Elsberg, under the term of dysæsthesia, makes two principal divisions—namely, first, disorders having reference to the quantity or intensity of the sensation; this embraces simple hyperæsthesia and simple anæsthesia. The second grand division relates to the quality of the sensation, and includes only paræsthesia or sensory delusions. These grand divisions are still further subdivided.
In fact, we have to do with exaltation of sensibility simply, with sometimes pain; second, with delusion of sensation; and, third, with lost or diminished sensation. For all practical purposes, therefore, we may adopt this arrangement, but should consider it as only provisional, as has been well observed by Schnitzler. These conditions are described under the terms hyperæsthesia, with or without pain; paræsthesia; anæsthesia.