<P> In humans there are two sets of pharyngeal muscles that form the pharynx, determining the shape of its lumen . These are arranged as an inner layer of longitudinal muscles and an outer circular layer . </P> <P> The upper portion of the pharynx, the nasopharynx, extends from the base of the skull to the upper surface of the soft palate . It includes the space between the internal nares and the soft palate and lies above the oral cavity . The adenoids, also known as the pharyngeal tonsils, are lymphoid tissue structures located in the posterior wall of the nasopharynx . Waldeyer's tonsillar ring is an annular arrangement of lymphoid tissue in both the nasopharynx and oropharynx . </P> <P> Polyps or mucus can obstruct the nasopharynx, as can congestion due to an upper respiratory infection . The auditory tube, which connect the middle ear to the pharynx, opens into the nasopharynx at the pharyngeal opening of the auditory tube . The opening and closing of the auditory tubes serves to equalize the barometric pressure in the middle ear with that of the ambient atmosphere . </P> <P> The anterior aspect of the nasopharynx communicates through the choanae with the nasal cavities . On its lateral wall is the pharyngeal opening of the auditory tube, somewhat triangular in shape, and bounded behind by a firm prominence, the torus tubarius or cushion, caused by the medial end of the cartilage of the tube which elevates the mucous membrane . Two folds arise from the cartilaginous opening: </P>

What are the three parts of the pharynx and their functions