Veins on the surface of the heart.
The cricoid cartilage is shaped like a signet-ring; it is made of hyaline cartilage and tends to ossify. The broad, posterior part, called the lamina, is quadrangular in outline. Its upper border is occupied by a pair of oval, convex facets separated by a shallow notch; these facets articulate with the bases of the arytenoid cartilages. The posterior surface of the lamina is divided by a median ridge into two areas which give origin to the posterior cricoarytenoid muscles. The median ridge itself gives attachment to a tendinous band which proceeds upwards from the longitudinal fibres of the esophagus. The anterior part of the cricoid cartilage is the arch. Its upper border slopes rapidly upwards as it passes backwards to the lamina, and gives attachment to the cricothyroid ligament and cricovocal membrane.
The facet for the thyroid is on the side of the ring at the junction of arch and lamina. The lower border of the ring is horizontal, and is connected to the first tracheal ring by the cricotracheal ligament; and the inner surface of the ring is lined with mucous membrane.
The arch of the cricoid cartilage lies below the anterior part of the thyroid cartilage, but the lamina is received into the interval between the posterior portions of the thyroid laminae.