LARYNX, THE (Gr. larynx), is the organ of voice, and takes a part in the respiratory process, as all air passing either to or from the lungs must pass through it. It is a com plex piece of mechanism, resembling a box composed of pieces of cartilage, which may be moved on each other, and inclosing the membranous bands (the chorclie vocales) by which the vocal vibrations are produced.
It is situated between the trachea, or windpipe, and the base of the tongue, at the upper and front part of the neck, where it forms a considerable projection (especially in men) in the mesial line; and it opens superiorly into the pharynx, or throat, and inferiorly into the windpipe.
The cartilages of which the skeleton of the larynx is composed are five in number— viz., the thyroid and the cricoid cartilages, the epiglottis, and the two arytenoid carti lages.
The thyroid (Gr. shield-like) cartilage consists of two square plates of cartilage united in front at an acute angle, which forms the projection which is commonly known as the pomum Adami, or Adam's apple. Each of these plates is prolonged at the upper and lower posterior corners. The thyroid cartilage forms almost the whole of the anterior and lateral walls of the larynx.
The cricoid (Gr. ring-like) cartilage is a ring whose lower margin is parallel to the first ring of the trachea, to which it is united by fibrous membrane. Its upper border is connected in front with the lower border of the thyroid cartilage by a thick yellow fibrous tissue. It presents two articular surfaces on either side, viz., a lower one, which articulates with the inferior cornua of the thyroid cartilage, and an upper one, which is oval in form, and supports an arytenoid cartilage. The arytenoid (Gr. ladle like) carti lages are pyramidal bodies-resting on the oval articular surfaces at the upper and pos terior part of the cricoid cartilage. When in, situ, they present a condave posterior surface. From their connection with the vocal cords, and from their great mobility as com pared with the two larger cartilages, the arytenoids play a very important part in the mechanism of the larynx. The epiglottis is a very flexible cartilaginous valve, situated at the base of the tongue, and covering the opening of the larynx. Its direction is ver
tical, except during deglutition, when it becomes horizontal. It is attached inferiorly by a kind of pedicle to the angle of the thyroid cartilage. Upon removing the investing mucous membrane, the cartilage is found to be perforated by numerous foramina. Each perforation admits some fasciculi, of yellow, elastic, ligamentous tissue, which expands on its anterior aspect, and secures the return of the epiglottis to its vertical position, independently of any muscular action. Such is the skeleton of the larynx, which hangs from the hyoid bone, with which it is connected by the thyro-hyoid liga ment and certain muscles.
The various cartilages which have been described are connected to one another by ligaments, the chief of which are those known as the true and false vocal cords. In their quiescent state, the true vocal cords do not lie parallel to each other, but converge from behind forwards. The length of the vocal cords is greater in the adult male thou in the adult female, in the ratio of three to two. In infancy, they are very short, and increase regularly from that period to the age of puberty. The mucous membrane of the larynx is part of the great respiratory tract (see Mucous MEMBRANE), and is remark able for its great sensibility.
The length of the chink or aperture of the glottis, which is directed horizontally from before backwards, varies, like the vocal cords, until the period of puberty, when its length, in the male, undergoes a sudden devolopment, while in the female it remains stationary. In the adult male, it is about eleven lines in length.
The larynx is provided with two sets of muscles, viz., the extrinsic, by which the whole organ is elevated or depressed, and the intrinsic, which regulate the movements of the various segments of the organ in relation to one another. By the action of these latter muscles, aided, in some cases, by the extrinsic muscles, the tension of the vocal cords may be increased or diminished, and the size of the opening of the glottis regulated at will.