These two small club-shaped cartilages (Fig. 8.214) lie anterior to the corniculate cartilages and are suspended in the part of the fibro-elastic membrane of the larynx that attaches the arytenoid cartilages to the lateral margin of the epiglottis.
The thyrohyoid membrane is a tough fibro-elastic ligament that spans between the superior margin of the thyroid cartilage below and the hyoid bone above (Fig. 8.215). It is attached to the superior margin of the thyroid laminae and adjacent anterior margins of the superior horns, and ascends medial to the greater horns and posterior to the body of the hyoid bone to attach to the superior margins of these structures.
An aperture in the lateral part of the thyrohyoid membrane on each side is for the superior laryngeal artery, the internal branch of the superior laryngeal nerve, and lymphatics.
The posterior borders of the thyrohyoid membrane are thickened to form the lateral thyrohyoid ligaments. The membrane is also thickened anteriorly in the midline to form the median thyrohyoid ligament.
Occasionally, there is a small cartilage (triticeal cartilage) in each lateral thyrohyoid ligament.
The hyo-epiglottic ligament (Fig. 8.215) extends from the midline of the epiglottis, anterosuperiorly to the body of the hyoid bone.
The cricotracheal ligament (Fig. 8.215) runs from the lower border of the cricoid cartilage to the adjacent upper border of the first tracheal cartilage.
Fibro-elastic membrane of the larynx
The fibro-elastic membrane of the larynx links together the laryngeal cartilages and completes the architectural framework of the laryngeal cavity. It is composed of two parts—a lower conus elasticus and an upper quadrangular membrane.
The conus elasticus (Fig. 8.216) is attached to the arch of cricoid cartilage and extends superiorly to end in a free upper margin within the space enclosed by the thyroid cartilage. On each side, this upper free margin attaches: anteriorly to the thyroid cartilage, and posteriorly to the vocal processes of the arytenoid cartilages.
The free margin between these two points of attachment is thickened to form the vocal ligament, which is under the vocal fold (true vocal cord) of the larynx.
The conus elasticus is also thickened anteriorly in the midline to form a distinct median cricothyroid ligament, which spans the distance between the arch of cricoid cartilage and the inferior thyroid notch and adjacent deep surface of the thyroid cartilage up to the attachment of the vocal ligaments.
In emergency situations, when the airway is blocked above the level of the vocal folds, the median cricothyroid ligament can be perforated to establish an airway. Except for small vessels and the occasional presence of a pyramidal lobe of the thyroid gland, normally there are few structures between the median cricothyroid ligament and skin.
The quadrangular membrane on each side runs between the lateral margin of the epiglottis and the anterolateral surface of the arytenoid cartilage on the same side (Fig. 8.217). It is also attached to the corniculate cartilage, which articulates with the apex of arytenoid cartilage.
Each quadrangular membrane has a free upper margin, between the top of the epiglottis and the corniculate cartilage, and a free lower margin. The free lower margin is thickened to form the vestibular ligament under the vestibular fold (false vocal cord) of the larynx.
The vestibular ligament is attached posteriorly to the superior depression on the anterolateral surface of the arytenoid cartilage and anteriorly to the thyroid angle just superior to the attachment of the vocal ligament.