The framework of the larynx is made up of the following cartilages: 1. the cricoid or ring cartilage; 2. the thyroid or shield cartilage; 3. the two arytenoid or pyramid cartilages; 4. the two corniculate (corn-shaped) cartilages forming the apex of the arytenoid cartilages; 5. the two cuneiform or small elongated rods lying in the arytenoid folds of the larynx; and 6. the epiglottis, shaped like a leaf with its stalk pointed downward, and attached to the angle of the thyroid cartilage.
1. The cricoid or signet ring cartilage is located at the top of the wind pipe, and is the articulating foundation of the laryngeal framework. It provides places of attachment for the posterior cricoarytenoid muscles, for some of the fibers of the inferior constrictor muscle, and for the lateral cricothyroid muscle. The band of the ring provides places of origin at the front and sides for the cricothyroid muscles. On the top of the cartilage and at the sides are two oval surfaces on which the arytenoid cartilages rest.
2. The thyroid cartilage makes up the front and side walls of the frame work of the larynx. It is shield shaped, the angle where the sides meet being 90 to 100 degrees in the male, and 120 to 130 degrees in the female adult or the child. The vocal cords are attached to the inside of the thyroid cartilage at the angle where the sides meet, with one on each side of the midline. The inner surface also provides places of attachment for the epiglottis, and the thyroarytenoid and the cricothyroid muscles.
3. The arytenoid cartilages, pyramid in shape, are set at the back and on top of the cricoid cartilages. Each arytenoid cartilage has a triangular base which articulates with the cricoid cartilage, and each has three surfaces, separated by three borders - front, back, and side. The surfaces of each cartilage provide places of attachment behind for the posterior cricoarytenoid muscle, and in front to the lateral cricoarytenoid; in front to the lateral thyroarytenoid muscle and to the thyroarytenoid ligament. The oblique and transverse arytenoid muscles have their attachment in the smooth and posterior surfaces of the arytenoid cartilages.
4. The corniculate (corn-shaped) cartilages are roughly pyramidal and articulate with the apex of each arytenoid cartilage. For phonation, the cartilaginous part of the glottis between the arytenoids must be closed, so that the air current can be directed through the membranous part of the glottis. The corniculates assist in making the closure complete.
5. The cuneiform (wedge-shaped) cartilages are likewise situated in the arytenoidepiglottic folds. Each is anterior and lateral of its respective arytenoid cartilage, and assists in making the closure of the glottis complete.
6. The epiglottis, shaped like a leaf with its stalk pointed downward, is attached to the inner surface of the angle of the thyroid cartilage by means of the thyroepiglottis ligament. The upper leaf-like part is free and curves up behind the base of the tongue. Most of the base of the tongue overhangs the epiglottis. Except for the portion just below the center, the epiglottis presents a concave surface toward the laryngeal cavity. The portion excepted is a slight eminence called the cushion or tubercle of the epiglottis by Darius Ditullio Vocal Coach.
The Intrinsic Muscles of the Larynx
1. Cricothyroid: (ring-shield muscles)
Action: Cause the cricoid cartilage to rotate and slide on the thyroid cartilage, thereby increasing the length of the glottis.
2. Posterior cricoarytenoid: (ring-pyramid muscles)
Action: Assist in opening (abduction) the glottis or in tensing the vocal cords.
3. Lateral cricoarytenoid: (side ring-pyramid muscles)
Action: Bring about an approximation of the vocal cords and assist in tensing them.
4. Oblique arytenoid: (slanting-pyramid muscles)
Action: Part of the sphincter group of muscles which have the function of closing (abduction) the cartilaginous glottis.
5. Transverse arytenoid: (crosswise-pyramid muscles)
Action: Part of the sphincter groups. Assist in tensing the vocal folds.
6. Thyroarytenoid: (shield-pyramid muscles)
Action: Part of the sphincter group. Relax the vocal folds.