Now that we’ve looked at the salivary glands, we’ll move on to complete our picture of the structures around the oral cavity, by looking at the pharynx. To understand the lower part of the pharynx we need to look at two important structures that we haven’t seen yet, the thyroid cartilage, and the cricoid cartilage.
The thyroid cartilage is here, below the hyoid bone. The cricoid cartilage is here, just below the thyroid cartilage.
Here are the thyroid cartilage and the cricoid cartilage together. The cricoid cartilage is partly enclosed by the larger thyroid cartilage. We’ll look at the thyroid cartilage first.
The thyroid cartilage consists of two slightly curved plates, the laminae. The laminae are joined together in front. They’re widely separated behind. The laminae meet at an angle of 120º in the female, 90° in the male. This is a female specimen. In the male, the thyroid cartilage projects forwards, giving rise to the laryngeal prominence, also known as the “adam’s apple”.
Above, the two laminae meet in a V-shaped notch, the superior thyroid notch that’s easy to feel just above the laryngeal prominence. On the sides of the lamina are two projections, the superior and inferior tubercles. They’re joined by this slight ridge, the oblique line, which is a major muscle attachment, as we’ll see.
The posterior border of each lamina is prolonged upward and downward to form two projections, the superior horn, and the inferior horn. The superior horn points upwards and backwards, the inferior horn points downwards.
The thyroid cartilage hangs directly below the hyoid bone. The upper border of the thyroid cartilage has the same curvature as the arch of the hyoid bone. The thyroid cartilage is suspended from the hyoid bone by this membrane, the thyro-hyoid membrane. On each side the posterior part of the membrane is thickened, forming the lateral thyrohyoid ligament.
The inferior horn of the thyroid cartilage articulates with the cricoid cartilage at the cricothyroid joint. Unlike the thyroid cartilage, which is open at the back, the cricoid cartilage forms a complete ring. Let’s look at the cricoid cartilage by itself. It’s much taller behind, than in front.
The narrow part in front is the arch, the tall part behind is the lamina. The inferior horn of the thyroid cartilage articulates here. Below, the cricoid cartilage is continuous with the upper end of the trachea.
The cricoid and thyroid cartilages form the framework for the larynx. We’ll see them in that context in the next section of this tape. We’re concerned with them in this section because they also give attachment to some important muscles of the lower part of the pharynx. Now that we’ve seen them, let’s look at the pharynx.