Cricoid
The cricoid cartilage, or simply cricoid, is the only complete ring of cartilage around the trachea. It sits just inferior to the thyroid cartilage in the neck, and is joined to it medially by the cricoythroid ligament and postero-laterally by the cricothyroid joints. Inferior to it are the rings of cartilage around the trachea (which are not continuous - rather they are C-shaped with a gap posteriorly). The cricoid is joined to the first tracheal ring by the cricotracheal ligament, and this can be felt as a more yielding area between the firm thyroid cartilage and firmer cricoid.
It is also anatomically related to the thyroid gland; although the thyroid isthmus is inferior to it, the two lobes of the thyroid extend superiorly on each side of the cricoid as far as the throid cartilage above it.
The posterior part of the cricoid is slightly broader than the anterior and lateral parts, and is called the lamina, while the anterior part is the band; this may refer to the common comparison made between the cricoid and a signet ring.
The function of the cricoid is to provide attachments for the various muscles, cartilages, and ligaments involved in opening and closing the airway and in speech production.
It is made of hyaline cartilage, and so can become calcified or even ossified, particularly in old age.