On each side, the vestibular ligament of the quadrangular membrane is separated from the vocal ligament of the cricothyroid ligament below by a gap. Because the vestibular ligament attaches to the anterolateral surface of the arytenoid cartilage and the vocal ligament attaches to the vocal process of the same cartilage, the vestibular ligament is lateral to the vocal ligament when viewed from above (Fig. 8.218).
The joints between the inferior horns of the thyroid cartilage and the cricoid cartilage, and between the cricoid cartilage and arytenoid cartilages are synovial. Each is surrounded by a capsule and is reinforced by associated ligaments. The cricothyroid joints enable the thyroid cartilage to move forward and tilt downward on the cricoid cartilage (Fig. 8.219).
Because the vocal ligaments pass between the posterior aspect of the thyroid angle and the arytenoid cartilages that sit on the lamina of cricoid cartilage, forward movement and downward rotation of the thyroid cartilage on the cricoid cartilage effectively lengthens and puts tension on the vocal ligaments.
The crico-arytenoid joints between articular facets on the superolateral surfaces of the cricoid cartilage and the bases of the arytenoid cartilages enable the arytenoid cartilages to slide away or toward each other and to rotate so that the vocal processes pivot either toward or away from the midline. These movements abduct and adduct the vocal ligaments (Fig. 8.220).
Cavity of the larynx
The central cavity of the larynx (Fig. 8.221) is tubular and lined by mucosa. Its architectural support is provided by the fibro-elastic membrane of the larynx and by the laryngeal cartilages to which it is attached.
The superior aperture of the cavity (laryngeal inlet) opens into the anterior aspect of the pharynx just below and posterior to the tongue (Fig. 8.221A):
Its anterior border is formed by mucosa covering the superior margin of the epiglottis.
Its lateral borders are formed by mucosal folds (ary-epiglottic folds), which enclose the superior margins of the quadrangular membranes and adjacent soft tissues, and two tubercles on the more posterolateral margin of the laryngeal inlet on each side mark the positions of the underlying cuneiform and corniculate cartilages.
Its posterior border in the midline is formed by a mucosal fold that forms a depression (interarytenoid notch) between the two corniculate tubercles.
The inferior opening of the laryngeal cavity is continuous with the lumen of the trachea, is completely encircled by the cricoid cartilage, and is horizontal in position unlike the laryngeal inlet, which is oblique and points posterosuperiorly into the pharynx. In addition, the inferior opening is continuously open, whereas the laryngeal inlet can be closed by downward movement of the epiglottis.
Two pairs of mucosal folds, the vestibular and vocal folds, which project medially from the lateral walls of the laryngeal cavity, constrict it and divide it into three major regions—the vestibule, a middle chamber, and the infraglottic cavity (Fig. 8.221B):
The vestibule is the upper chamber of the laryngeal cavity between the laryngeal inlet and the vestibular folds, which encloses the vestibular ligaments and associated soft tissues.
The middle part of the laryngeal cavity is very thin and is between the vestibular folds above and the vocal folds below.
The infraglottic space is the most inferior chamber of the laryngeal cavity and is between the vocal folds (which encloses the vocal ligaments and related soft tissues) and the inferior opening of the larynx.