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The cricoid cartilage is the ring-shaped cartilage at the lower part of the larynx, above the trachea. Unlike the shield-shaped thyroid cartilage, it forms a complete cartilaginous ring, with a broader posterior plate. It helps support the airway and provides articulations and muscle attachments within the laryngeal framework.^[ref]

The ring geometry and its connections matter mechanically. Laryngeal muscles move connected cartilages to alter vocal-fold position and tension; those motions can change the opening through which air passes. A static anatomical ring therefore participates in an actively controlled valve and sound-producing assembly.

The cricothyroid muscle changes the relation of the cricoid cartilage and thyroid cartilage, helping lengthen and tense the vocal folds. This contributes to pitch control during phonation. It is supplied by the external branch of the superior laryngeal nerve, a distinctive relation among intrinsic laryngeal muscles.

The thyroid cartilage is the large shield-like cartilage forming much of the anterior and lateral framework of the larynx. Its two broad plates meet at the front, and its connections provide support and attachment for tissues involved in airway protection and voice production.^[ref]

Movement at its relationship with the cricoid cartilage helps alter vocal-fold tension. Changing tension changes the mechanical conditions for oscillation, while airflow supplies energy. The cartilage is distinct from the nearby thyroid gland: sharing the word “thyroid” does not make the laryngeal supporting structure a hormone-secreting gland.