The pharynx is that part of the alimentary canal and respiratory tract, which is a connecting link between the cavity of the nose and mouth and the oesophagus and trachea. It stretches from the level of the base of the skull to that of the sixth or seventh cervical vertebra. The space within the pharynx is the pharyngeal cavity (cavitas pharyngis). The pharynx is situated behind the nasal and oral cavities and the larynx and in front of the basilar part of the occipital bone and the upper six cervical ver­tebrae. In accordance with the organs situated in front of the pharynx, three parts can be distinguished in it: pars nasalis, pars oralis, and pars laryngea. The superior wall of the pharynx, which adjoins the base of the skull, is called the vault of the pharynx (fornix pharyngis). The nasal part of the pharynx, or the nasopharynx (pars nasalis phar­yngis) (Fig. 190) is a purely respiratory part functionally. As distinct from the other parts of the pharynx, its walls do not collapse because they are immobile. The anterior wall of the nasal part is occupied by the choanae. On either lateral wall is a funnel-shaped pharyngeal opening of the auditory tube (part of the middle ear), ostium pharyngeum tubae. Superiorly and posteriorly the opening of the tube is bounded by torus tubarius formed due to the projec­tion of the cartilage of the auditory tube here. At the junction of the superior and posterior pharyngeal walls on the midline is an accumulation of lymphoid tissue, the pharyngeal tonsil, or adenoids (tonsilla pharyngea s. adenoidea) (in adults it is hardly noticeable, or disappears entirely). Another accumula­tion of lymphoid tissue, but paired, is located between the pharyngeal open­ing of the tube and the soft palate; this is the tube tonsil (tonsilla tubaria). Thus, almost a complete ring of lymphoid structures is found at the entry into the pharynx: the lingual tonsil, two palatine tonsils, two tube tonsils, and one pharyngeal tonsil (Pirogov's lymphoepithelial ring). The oral part (pars oralis) is the middle part of the pharynx communicat­ing with the oral cavity in front through the isthmus faucium, its posterior wall corresponds to the third cervical vertebra. The oral part is mixed in function because the alimentary and respiratory tracts intersect here. The intersection formed during the development of the respiratory organs from the wall of the primary gut. The nasal and oral cavities originated from the primary naso-oral bay, the nasal cavity being situated superiorly or as if dorsally in relation to the oral cavity, whereas the pharynx, trachea, and lungs arose from the ventral wall of the foregut. The cephalic part of the alimentary tract is, consequently, located between the nasal cavity (superiorly and dorsally) and the respiratory tract (ventrally). As a result the alimen­tary and respiratory tracts intersect in the pharynx (see Fig. 233). The laryngeal part {pars laryngea) begins behind the trachea and extends from the opening into the larynx to the opening into the oesophagus. In a state of rest, when there is no swallowing, the anterior and posterior walls of this part remain in contact and separate only when food passes in it, that is why the laryngeal part cannot be seen during laryngoscopy if the larynx is not pulled forward. On the anterior wall is the opening into the larynx bound­ed in front by the epiglottis and on the sides by the aryepiglotic folds {plicae aryepiglotticae). On either side of the folds lie paired pear-shaped fossae in the pharyngeal wall (recessus piriformes). The foundation of the pharyngeal wall is a well developed layer of fibrous tissue. This fibrous coat is lined in­side with mucous membrane (mucous coat) and covered from the outside by a muscular coat. The muscular coat is in turn covered by a thinner layer of fibrous tissue connecting the pharyngeal wall with the adjoining organs; superiorly this fibrous tissue passes on to the buccinator muscle and is called the buccopharyngeal fascia. The fibrous coat of the pharynx, pharyngobasilar fascia (fascia pharyngobasilaris) is attached above to the basal part of the occipital bone and to the other bones of the base of the skull and stretches forward to the medial pterygoid plate. The fibrous coat is especially well developed in the upper part where it is only partly covered by the superior constrictor. The mucous coat of the nasal part of the pharynx is covered with ciliated epithelium in accordance with the respiratory function of this part of the pharynx, whereas in the inferior parts it is covered with stratified squamous epithelium. The mucous coat of the inferior parts of the pharynx fuses with the underlying tissue and acquires a smooth surface, which pro­motes gliding of the bolus during swallowing. This is also aided by the se­cretion of mucous glands embedded in the mucosa and by the pharyngeal muscles arranged longitudinally (dilators) and circular (constrictors). The circular layer is much stronger and consists of three constrictors (Figs. 191 and 192) arranged in three storeys: the superior constrictor muscle of the pharynx (m. constrictor pharyngis superior), the middle constrictor muscle of the pharynx (m. constrictor pharyngis medius), and the inferior constrictor muscle of thephar-ynx (m. constrictor pharyngis inferior). Arising on different points, namely on the bones of the base of the skull (pharyngeal tubercle of the occipital bone and the pterygoid process of the sphenoid bone), on the mandible (the mylo­hyoid line), on the root of the tongue, on the hyoid bone, and on the pharyn­geal cartilages (thyroid and cricoid) the fibres of the muscles on each side pass backward and join each other to form a seam on the midline of the pharynx, the raphe of the pharynx (raphe pharyngis). The lower fibres of the inferior pharyngeal constrictor are, closely connected with the muscle fibres of the oesophagus. The longitudinal muscle fibres of the pharynx run in the follow­ing two muscles. The stylopharyngeus muscle (m. stylopharyngeus) arises from the sty­loid process and descends to be inserted partly in the pharyngeal wall itself and partly on the superior edge of the thyroid cartilage. The palatopharyngeus muscle (m. palatopharyngeus) is described above (see "Soft Palate"). The act of swallowing, deglutition. Since the respiratory and digestive tracts intersect in the pharynx, special devices exist, which separate these two tracts during swallowing. By contraction of the tongue muscles the bolus is pressed against the hard palate by the dorsum of the tongue and then pushed through the fauces. During this process, the soft palate is pulled upward (by contraction of the levator veli palatini and the tensor veli palatini muscles) and brought nearer to the posterior pharyngeal wall (by contraction of the palatopharyngeus muscle). In this manner, the nasal (respiratory) part of the pharynx is completely separated from the oral part. At the same time, the suprahyoid muscles pull the pharynx upward, while the root of the tongue is pulled downward by contraction of the hyoglossus muscle; the root of the tongue presses against the epiglottis and depresses it and closes the open­ing into the larynx (into the respiratory tract) in this way. Then the pharyn­geal constrictors contract in succession as a result of which the bolus is pushed toward the oesophagus. The longitudinal pharyngeal muscles act as elevators, they pull the pharynx to meet the bolus. The pharynx receives nutrients mainly from the ascending pharyngeal artery and the branches of the facial and maxillary arteries from the external carotid artery. Venous blood drains into a plexus situated on the muscular coat of the pharynx and then into the system of the internal jugular vein by way of the pharyngeal veins. The lymph flows into the deep cervical and retropharyngeal lymph nodes. The pharynx is innervated from the pharyngeal plexus formed by branches of the glossopharyngeus and vagus nerves and branches of the sympathetic trunk. The sensory innervation is conducted along the glos­sopharyngeus and vagus nerves; the muscles of the pharynx are innervated by the vagus, except for the stylopharyngeus muscle, which is innervated by the glossopharyngeus nerve.