The abundant lymphoid tissue in the pharynx forms an incomplete tonsillar ring around the superior part of the pharynx. The lymphoid tissue is aggregated in certain regions to form masses called tonsils. The pharyngeal tonsil (commonly called the adenoid when enlarged) is in the mucous membrane of the roof and posterior wall of the nasopharynx. Extending inferiorly from the medial end of the pharyngotympanic tube is a vertical fold of mucous membrane, the salpingopharyngeal fold. It covers the salpingopharyngeus muscle, which opens the pharyngeal orifice of the pharyngotympanic tube during swallowing. The collection of lymphoid tissue in the submucosa of the pharynx near the nasopharyngeal opening, or orifice of the pharyngotympanic tube, is the tubal tonsils. Posterior to the torus of the pharyngotympanic tube and the salpingopharyngeal fold is a slit-like lateral projection of the pharynx, the pharyngeal recess, which extends laterally and posteriorly.