VOICE is the sound produced by the vibrations of the vocal cords, two ligaments or bands of fibrous elastic tissue situated in the larynx. It is to be distinguished from speech, which is the production of articulate sounds intended to express ideas. (See SINGING; and for speech see PHONETICS.) Physiological Anatomy.—The larynx is a valve guarding the entrance to the trachea. In man it is used as the organ of voice.
It is situated in the neck, where it forms a well marked promi nence in the middle line (see details under RESPIRATORY SYSTEM).
It consists of a framework of cartilages, connected by elastic mem branes or ligaments, and it contains two important structures known as vocal cords. The latter, if brought into apposition can be blown apart by an expiratory blast of air; there is con sequently a fall in pressure in the trachea, which allows the cords to come into contact again; repetition of this action allows puffs of air to escape rhythmically from the larynx into the pharynx and out by the mouth or nose with the production of a note.
The cartilages form the framework of the larynx. They consist of three single pieces (the thyroid, the cricoid and the cartilage of the epiglottis) and of three pairs (two arytenoids, two cornicula laryngis or cartilages of Santorini, and twc cuneiform cartilages or cartilages of Wris berg), see figs. I and 2. The epiglottis, the cornicula laryngis, the cuneiform cartil ages and the apices of the arytenoids are composed of yellow or elastic fibro-cartil age, whilst the cartilage of all the others is of the hyaline variety, resembling that of the costal or rib cartilages. These cartilages are bound together by ligaments, some of which are seen in figs. I and 2, whilst the remainder are represented in fig. 3. The structures specially concerned in the pro duction of voice are the inferior thyro arytenoid folds, or true vocal cords. These are composed of fine elastic fibres attached behind to the anterior projection of the base of the arytenoid cartilages, processes vocalis, see fig. 3, and in front to the mid
dle of the angle between the wings or laminae of the thyroid cartilage. They are continuous with the lateral cricothyroid liga ments which form the conus elasticus, see fig. 3.
The cavity of the larynx is divided into an upper and lower portion by the narrow aperture of the glottis or chink between the edges, of the true vocal cords, the ritna glottidis. Immediately above the true vocal cords, between these and the false vocal cords, there is on each side a recess or pouch termed the ventricle of Morgagni, and opening from each ventricle there is a still smaller recess, the laryngeal saccule, which passes for the space of half an inch between the superior vocal cords inside and the thyroid cartilage outside, reaching as high as the upper border of that cartilage at the side of the epiglottis. The upper aperture of the larynx is bounded in front by the epiglottis, behind by the summits of the arytenoid cartilages and on the sides by two folds of mucous membrane, the aryteno-epiglottic folds.
The rime glottidis, between the true vocal cords, in the adult male measures about 23 mm., or nearly an inch from before back wards, and from 6 to 12 mm. across its widest part, according to the degree of dilation. In fe males and in males before pu berty the antero-posterior diame ter is about 17 mm. and its trans verse diameter about 4 mm. The vocal cords of the adult male are in length about 15 mm., and of the adult female about I r mm. The larynx is lined with a layer of epithelium, which is closely ad herent to underlying structures, more especially over the true vo cal cords. The cells of the epithe lium, in the greater portion of the larynx, are of the columnar cili ated variety, and by the vibra tory action of the cilia mucus is driven upwards, but over the true vocal cords the epithelium is squamous. Numerous mu cous glands exist in the lining membrane of the larynx, more especially in the epiglottis. In each laryngeal pouch there are from sixty to seventy such glands.