PHARYNX, in anatomy, the cavity into which both the nose and mouth lead, which is prolonged into the oesophagus or gullet below, and from which the larynx or air tube comes off below and in front ; it therefore serves as a passage both for food and air. The back and sides of the cavity are formed by the three con strictor muscles of the pharynx, each of which overlaps the outer surface of the one above it, and these are lined internally by thick mucous membrane. Above, the pharynx is attached firmly to the base of the skull and the internal pterygoid plates, so that this part cannot collapse, but below the anterior and posterior walls are in contact, and a transverse section of the pharynx is a mere slit.
From the front wall, on a level with the floor of the nose and roof of the mouth, a slanting shelf of muscular and glandular tissue covered with mucous membrane, projects downward and backward into the cavity, and divides it into an upper part or naso-pharynx and a lower or oral pharynx (see fig.). This shelf is the soft palate, and from the middle of its free border hangs a worm-like projection, the uvula. The whole of the front wall of the naso-pharynx is wanting, and here the cavity opens into the nose through the posterior nasal apertures (see OLFACTORY SYS TEM). On each side of the naso-pharynx, and therefore above the soft palate, is the large triangular opening of the Eustachian tube through which air passes to the tympanum (see EAR). Behind this opening, and reaching up to the roof of the naso-pharynx, is a mass of lymphoid tissue, most marked in children, known as the pharyngeal tonsil. This tissue hypertrophies in the disease known as "adenoids." The oral pharynx communicates with the naso-pharynx behind the free edge of the soft palate. Above and in front it is continu ous with the cavity of the mouth, and the demarcation between the two is a ridge of mucous membrane on each side running from the soft palate to the side of the tongue, and caused by the pro jection of the palato-glossus muscle (anterior pillar of the fauces). About half an inch behind this ridge is another, made by the palato-pharyngeus muscle, which gradually fades away in the side of the pharynx below (posterior pillar of the fauces). Be tween the two pillars is the fossa (tonsilar sinus) in which the tonsil lies.
The Tonsil is an oval mass of lymphoid tissue covered by mu cous membrane which dips in to form mucous crypts; externally its position nearly corresponds to that of the angle of the jaw. It
is very vascular, deriving its blood from five neighbouring arteries. Below the level of the tonsil the anterior wall of the pharynx is formed by the posterior or pharyngeal surface of the tongue (q.v.), while below that is the epiglottis and upper opening of the larynx which is bounded laterally by the aryteno-epiglottic folds (see RESPIRATORY SYSTEM). On the lateral side of each of these folds is a pear-shaped fossa known as the sinus pyriformis. Below this the pharynx narrows rapidly until the level of the lower border of the cricoid cartilage in front and of the sixth cervical vertebra behind is reached ; here it passes into the oesophagus, having reached a total length of about five inches.
The mucous membrane of the naso-pharynx, like that of the rest of the respiratory tract, is lined by ciliated columnar epi thelium, but in the oral pharynx the epithelium is of the stratified squamous variety. Numerous racemose glands are present (see GLANDS; TISSUES), as well as patches of lymphoid tissue espe cially in childhood. Outside the mucous membrane and separating it from the constrictor muscles is the pharyngeal aponeurosis, which blends above with the periosteum of the base of the skull.