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Largest of nine cartilages that make up the laryngeal skeleton

The thyroid cartilage is the largest of the nine cartilages that make up the laryngeal skeleton, the cartilage structure in and around the trachea that contains the larynx. It does not completely encircle the larynx (only the cricoid cartilage encircles it).

The thyroid cartilage is a hyaline cartilage structure that sits in front of the larynx and above the thyroid gland. The cartilage is composed of two halves, which meet in the middle at a peak called the laryngeal prominence, also called the Adam's apple. In the midline above the prominence is the superior thyroid notch. A counterpart notch at the bottom of the cartilage is called the inferior thyroid notch. The two halves of the cartilage that make out the outer surfaces extend obliquely to cover the sides of the trachea. The posterior edge of each half articulates with the cricoid cartilage inferiorly at a joint called the cricothyroid joint. The most posterior part of the cartilage also has two projections upwards and downwards. The upper projection is called the superior horn (cornu), and the lower is called the inferior horn. The superior horn is long and narrow, backward, and medialward, and ends in a conical extremity, which gives attachment to the lateral thyrohyoid ligament. The inferior horn is short and thick; it is directed downward, with a slight inclination forward and medialward, and presents, on the medial side of its tip, a small oval articular facet for articulation with the side of the cricoid cartilage. The entire superior edge of the thyroid cartilage is attached to the hyoid bone by the thyrohyoid membrane. The thyroid cartilage is found between the levels of the C4 to C5 vertebrae. The oblique line is a line on the thyroid cartilage. It marks the upper lateral borders of the thyroid gland. Two muscles originate along the line, the thyrohyoid muscle and inferior pharyngeal constrictor. The sternothyroid inserts along the line. Movement of the cartilage at this joint produces a change in tension at the vocal folds, which in turn produces variation in voice.

The thyroid cartilage may contain a variant foramen, known as thyroid foramen, in up to 39% of individuals.

The thyroid cartilage forms the bulk of the front wall of the larynx. It protects the vocal folds ("vocal cords"), which are located directly behind it. When the angle of the thyroid cartilage changes relative to the cricoid cartilage, this changes the pitch of voice. The cartilage also serves as an attachment for several muscles.

The English term thyroid cartilage is derived from the Latin expression cartilago thyreoides. The latter is a translation of Ancient Greek χόνδρος θυρεοειδής, attested in the writings of the Greek physician Galen. while the ancient Greek word θυρεοειδής means shield like or shield shaped. The ancient Greek word θυρεός can be found in the Odyssey of Homer, and represented a large square stone that was put against the door to keep it shut. cartilago parmalis, were coined for the thyroid cartilage. In 16th century Italian anatomist Realdo Colombo's De re anatomica, while the name of the shield itself, i. e. scutum, is still being mentioned as a synonym for the thyroid cartilage.

In the various editions of the official Latin nomenclature (Nomina Anatomica, in 1998 rebaptized as Terminologia Anatomica), three different spellings can be found, i. e. cartilago thyreoidea. cartilago thyroidea and the previously mentioned cartilago thyreoides. The variant with the adjective thyreoidea (with the ending ea) would be a faulty rendering of Ancient Greek θυρεοειδής in Latin. Greek compounds ending in ειδής, when imported into Latin as a loanword, ended in ides. In the 17th century the non classical Latin form ideus/ idea/ideum for Greek ειδής/ ειδές came into use, mostly by French anatomist Jean Riolan the Younger. but after a list of recommendations/corrections was made forcing a greater resemblance between Latin and English orthography. Dorland's medical dictionary from 1948 but earlier works preferred the etymologically correct thyreoid cartilage. The official Latin veterinary nomenclature, Nomina Anatomica Veterinaria, has the form cartilago thyroidea, in common with the human Nomina Anatomica/Terminologia Anatomica, but allows (in contrast to the latter) cartilago thyreoidea as an alternative spelling.