<P> In humans the pharynx is part of the digestive system and also of the conducting zone of the respiratory system . (The conducting zone also includes the nostrils of the nose, larynx, trachea, bronchi, and bronchioles, and their function is to filter, warm, and moisten air and conduct it into the lungs .) The pharynx makes up the part of the throat situated immediately behind the nasal cavity, behind the mouth and above the esophagus and larynx . The human pharynx is conventionally divided into three sections: the nasopharynx, the oropharynx and the laryngopharynx . It is also important in vocalization . </P> <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>

Which part of the pharynx lies behind the nasal cavity