Page:EB1911 - Volume 28.djvu/189

Rh as that represented by 30 mm. of water. Such is a general conception of the mechanism of voice.

The cartilages form the framework of the larynx. They consist of three single pieces (the thyroid, the cricoid and the cartilage of 3.—Right Half of the Larynx, from a vertical and slightly oblique section; abt. two-thirds nat. size. 1, epiglottis; 2, arytenoid cartilage; 3, processus vocalis of arytenoid; 4, cricoid cartilage; 5, capsular thyro-hyoid ligament; 6, lateral crico-thyroid ligament; 7, posterior crico-thyroid ligament; 8 inferior thyro-arytn oid ligament, or true vocal cord; 9, thyroid cartilage; 10, superior thyro-arytenoid ligament, or false vocal chord; 11, thyro-ary-epiglottideus muscle; 12, middle thyro-hyoid ligament; 13, hyo-epiglottic ligament; 14, body of hyoid bone; 15, smaller cornu of hyoid bone. (From Krause.) the epiglottis) and of three pairs (two arytenoids, two cornicula laryngis or cartilages of Santorini, and two cuneiform cartilages or cartilages of Wrisberg), see figs. 1 and 2. The epiglottis, the cornicula laryngis, the cuneiform cartilages and the apices of the arytenoids are composed of yellow or elastic fibro-cartilage, 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. 1 and 2, whilst the remainder are represented in fig. 3. The ligaments specially concerned in the production of voice are the inferior thyro-arytenoid ligaments, or true vocal cords. These are composed of fine elastic fibres attached behind to the anterior projection of the base of the arytenoid cartilages, processus vocalis, 3 in fig. 3, and in front to the middle of the angle between the wings or laminae of the thyroid cartilage. They are practically continuous with the lateral crico-thyroid ligaments, 6 in 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 chords, the rima glottidis. Immediately above the true vocal cords, between these and the false vocal chords, there is on each side a recess or pouch termed the ventricle of Morgani, and opening from each ventricle there is a still smaller recess, the laryngeal pouch, which passes for the space of half an inch between the superior vocal chords inside and the thryoid cartilage outside, reaching as high as the upper border of that cartilage at the side of the epiglottis. The ventricles no doubt permit a free vibration of the true vocal cords. The upper aperture of the glottis is triangular, wide in front and narrow behind; and, when seen from above by means of the laryngoscope, it presents the view represented in fig. 4. The aperture is bounded in front by the epiglottis, e, behind by the summits of the arytenoid 4.—Laryngoscopic View of the Glottis. t, tongue; e, epiglottis; pe, pharyngo-epiglottis fold; g, pharyngo-laryngeal groove; ae, aryteno-epiglottis fold; c, cuneiform cartilage, or cartilage of Wrisberg; ar, arytenoid cartilage; r, inter-arytenoid fold; o, glottis; v, ventricle; ti, inferior or true vocal cord; ts, superior or false vocal cord. (From Mandl.) cartilages, ar, and on the sides by two folds of mucous membrane, the aryteno-epiglottis folds, ae. The rounded elevations corresponding to the cornicula laryngis and cuneiform cartilages, c, and also the cushion of the epiglottis, e, are readily seen in the laryngoscopic picture. The glottis, o, is seen in the form of a long narrow fissure, bounded by the true vocal cords, ti, whilst above them we have the false vocal cords, ts, and between the true and false cords the opening of the ventricle, v. The rima glottidis, between the true vocal cords, in the adult male measures about 23 mm., or nearly an inch from before backwards, and from 6 to 12 mm. across its widest part, according to the degree of dilatation. In females and in males before puberty the antero-posterior diameter is about 17 mm. and its transverse diameter about 4 mm. The vocal cords of the adult male are in length about 15 mm., and of the adult female about 11 mm. The larynx is lined with a layer of epithelium, which is closely adherent to underlying structures, more especially over the true vocal cords. The cells of the epithelium, in the greater portion of the larynx, are of the columnar ciliated variety, and by the vibratory action of the cilia mucus is driven upwards, but over the true

vocal cords the epithelium is squamous. Patches of squamous epithelium are also found in the ciliated tract above the glottis, on the under surface of the epiglottis, on the inner surface of the arytenoid cartilages, and on the free border of the upper or false cords. Numerous mucous glands exist in the lining membrane of the larynx, more especially in the epiglottis. In each laryngeal pouch there are sixty to seventy such glands, surrounded by fat.

We are now in a position to understand the action of the muscles of the larynx by which the vocal cords, forming the rima glottidis, 5.— Muscles of the left side of the larynx, seen from within; abt. two-thirds nat. size. 1, hyo-epiglottic ligament, seen in profile; 2, epiglottis; 3, aryteno-epiglottis muscle; 4, Santorini's cartilage; 5, oblique arytenoid muscle; 6, transverse arytenoid muscle, seen in profile; 7, posterior crico-arytenoid; 8, lateral crico-arytenoid; 9, lower cornu of thyroid cartilage cut through; 10, insertion of posterior portion of crico-thyroid muscle; 11, left lamina of thyroid cartilage cut through; 12, long thyro-epiglottic muscle (a variety); 13, inferior thyro-arytenoid; 14, thyro-epiglottic; 15, superior thyro-arytenoid; 16, median thyro-hyoid ligament. (From Krause.) can be tightened or relaxed, and by which they can be approximated or separated. Besides certain extrinsic muscles—sterno-hyoid, omohyoid, sterno-thyroid and thyro-hyoid—which move the larynx as a whole, there are intrinsic muscles which move the cartilages on each other. Some of these are seen in fig. 5. These muscles are (a) the crico-thyroid, (b) the posterior crico-arytenoid, (c) the lateral crico-arytenoid, (d) the thyro-arytenoid, (e) the arytenoid, and (f) the aryteno-epiglottidean. Their actions will be readily understood with the aid of the diagrams in fig. 6. (1) The crico-thyroid is a short thick triangular muscle, its fibres passing from the cricoid cartilage obliquely upwards and outwards to be inserted into the lower border of the thyroid cartilage and to the outer border of its lower horn. When the muscle contracts, the cricoid and thy roid cartilages are approximated. In this action, however, it is not the thyroid that is depressed on the cricoid, as is generally stated, but, the thyroid being fixed in position by the action of the extrinsic muscles, the anterior border of the cricoid is drawn upwards, whilst its posterior border, in consequence of a revolution around the axis uniting the articulations between the lower cornua of the cricoid and the thyroid, is depressed, carrying the arytenoid cartilages along with it. Thus the vocal cords are stretched. (2) The thyro-arytenoid has been divided by anatomists into two parts—one, the internal, lying close to the true vocal cord, and the other, external, immediately within the ala of the thyroid cartilage. Many of the fibres of the anterior portion pass from the thyroid cartilage with a slight curve (concavity inwards) to the processus vocalis at the base of the arytenoid cartilage. They are thus parallel with the true vocal cord, and when they contract the arytenoids are drawn forwards, carrying with them the posterior part of the cricoid and relaxing the vocal cords. Thus the thyro-arytenoids are the antagonists of the crico-thyroids. K. F. W. Ludwig has pointed out that certain fibres (portioary-vocalis) arise from the side of the cord itself and pass obliquely back to the processus vocalis. These will tighten the parts of the cord in front and relax the parts behind their points of attachment. Some of the fibres of the outer portion run obliquely upwards from the side of the crico-thyroid membrane, pass through the antero-posterior fibres of the inner portion of the muscle, and finally end in the tissue of the false cord. These fibres have been supposed to render the edge of the cord more prominent. Other fibres inserted into the processus vocalis will rotate slightly the arytenoid outwards, whilst a few passing up into the aryteno-epiglottidean folds may assist in depressing the epiglottis (Quain). (3) The posterior and lateral crico-arytenoid muscles have antagonistic actions, and may be considered together. The posterior arise from the posterior surface of the cricoid cartilage, and passing upwards and outwards are attached to the outer angle of the base of the arytenoid. On the other hand, the lateral arise from the upper border of the cricoid as far back as the articular surface for the arytenoid, pass backwards and upwards, and are also inserted into the outer angle of the base of the arytenoid before the attachment of the posterior crico-arytenoid. Imagine the pyramidal form of the arytenoid cartilages. To the inner angle of the triangular base are attached, as already described, the true vocal cords; and to the outer angle the two muscles in question. The posterior crico-arytenoids draw the outer angles backwards and inwards, thus rotating the inner angles, or processus vocalis, outwards, and, when the two muscles act, widening the rima glottidis. This action is opposed by the lateral crico-thyroids, which draw the outer angle forwards and outwards, rotate the inner angles inwards,