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segment (nasal portion), from the posterior margin of the septum of the nose at its inferior part horizontally backwards, measures 15 to 18 mm., and that of the middle segment, from the glossopalatine arches to the posterior wall, about 10 mm. Below that level, the anterior and posterior walls gradually approach one another, until, below the laryngeal orifice, they are in contact with one another.
The transverse width of the pharynx also varies considerably. Immediately below the base of the skull the cavity is wide, as there is on each side a deep recess, and it measures 45 mm., or nearly 2 inches.
Opposite the middle of the soft palate the cavity narrows, and measures transversely 25 mm., or 1 inch.
It again widens out below this level, and expands to a width of 35 mm., opposite the inferior margin of the laryngeal opening, where on each side there is a wide recess, called the piriform recess.
FIG. 901.-INTERIOR OF PHARYNX AND STRUCTURES IN RELATION TO ITS SIDE WALLS,
Cavum Pharyngis.-The cavity of the pharynx is partially intersected by the soft palate, which is attached anteriorly to the hard palate, and laterally to the side walls of the pharynx. This sheet, sloping obliquely backwards and downwards, cuts into the cavity of the pharynx (Fig. 901), and, falling short of the posterior wall, incompletely divides it into two, namely, an upper part, pars nasalis (O.T. naso-pharynx), and a lower part or pharynx proper. This lower portion is further subdivided into the pars oralis (O.T. oral pharynx), lying behind the mouth and tongue, and the pars laryngea (O.T. laryngeal pharynx), behind the larynx.
The aperture left between the soft palate and the posterior wall of the pharynx, through which the nasal part of the pharynx communicates with the inferior divisions of the cavity, is called the isthmus pharyngonasalis.
The pharynx presents seven openings by which it communicates with
neighbouring cavities (Fig. 901). These are the two choana (O.T. posterior nares) on the anterior wall of the pars nasalis, and the two tube auditivæ (O.T. Eustachian tubes) on its side walls; the isthmus of the fauces, leading into the mouth. from the oral part; the orifice of the larynx on the anterior wall of the laryngeal part of the cavity; and finally, the opening of the oesophagus at its inferior end.
Pars Nasalis (O.T. Naso-Pharynx) (Figs. 901 and 902).-Although morphologic ally and developmentally this is a portion of the true pharynx, it is functionally an annexe to the respiratory portion of the nasal cavities, and both anatomically and
A frontal section was made through the upper part of the head; this passed immediately in front of the posterior edge of the nasal septum, and extended into the mouth below. Through the choanz the nasal part of the pharynx is seen. The prominence of the posterior margin of the ostium phary geum of the auditory tube, and the lymph nodules constituting the pharyngeal tonsil, should be noted. The palatine arches and tonsils, and an unusually wide pharyngo-nasal isthmus, are also seen.
functionally it is distinctly marked off from the digestive tube. It differs from the rest of the pharynx in that its cavity remains, under all conditions, a distinct open chamber incapable of obliteration, owing to the fact that all its walls, with the single exception of the floor, are practically immovable.
The cavity of the pars nasalis is irregular in shape, and is enclosed by six walls-namely, anterior and posterior, right and left, a floor and a roof or vault.
These walls all merge into one another, and the lines of separation between them are arbitrary. Through the anterior wall, which slopes upwards and backwards, open choanæ (O.T. posterior nares), separated from each other by the nasal septum. margins of the choana form the line of separation between the pars nasalis and the cavity of the nose. This separation is occasionally marked by a furrow or fold on the side wall, called the naso-pharyngeal furrow.
The posterior wall is nearly vertical, and may be considered to extend upwards as far as to the level of the body of the sphenoid bone, where it becomes continuous with the I rounded vault forming the roof.
The roof lies under the body of the sphenoid, and on each side it extends downwards to the superior margin of the orifice of the auditory tube. It slopes from in front downwards and backwards to meet the posterior wall at the junction of the basilar part of the occipital and sphenoid bones, immediately anterior to the pharyngeal bursa-a small median recess in the pharyngeal wall, found constantly in the child and occasionally in the adult.
The side walls, right and left, are occupied by the pharyngeal opening of the auditory tube, and posterior to them, by a vertical slit-like depression leading into a recess, called the recessus pharyngeus (Rosenmülleri).
The floor is formed by the upper surface of the soft palate.
Between the floor and the posterior wall is the aperture, the isthmus pharyngonasalis, through which the pars nasalis communicates with the cavity of the pharynx proper. When the soft palate is raised, this communication becomes closed, by contact of the soft palate with the posterior wall, and the floor of the pars nasalis is complete.
A number of important structures are found in the walls of the pars nasalis. In the posterior part of the roof, and superior part of the posterior wall, there is a considerable accumulation of lymph tissue, known as the pharyngeal tonsil. It is most distinct in the child, and becomes indistinct, or entirely disappears, in adult life. It extends from the body of the sphenoid down as far as to the margin of the occipital bone, and, laterally, as far as to the superior part of the side wall. The mucous membrane which covers it is thickened and thrown into transverse folds.
In connexion with the inferior part of the pharyngeal tonsil, there is found, constantly in the child and occasionally in the adult, a small median recess which runs upwards and ackwards in the wall of the pharynx for some distance, and is known as the bursa pharyngea (Fig. 903). The origin and morphological significance of this pouch are not yet solved.
Enlargement of the lymph tissue here occurs frequently in children, and the swollen lymph nodules are known as adenoids. The enlargement may become so great as to fill up a great part of the cavity of the nasal part of the pharynx.
Ostium Pharyngeum Tube Auditive. On each side wall is placed the pharyngeal orifice of the auditory tube (O.T. Eustachian tube), an opening of a somewhat triangular form, with a characteristic infundibular or funnel-like appearance (Fig. 903). It is bounded superiorly and posteriorly by a prominent rounded ridge, the torus tubarius (O.T. Eustachian cushion). This ridge is due to the projection of the cartilage which surrounds the auditory tube superiorly and posteriorly, but is absent inferiorly and anteriorly. The prominence of the posterior margin (labium posterius) as contrasted with the anterior margin (labium anterius) of the orifice, and the direction of the tube itself, which runs posteriorly and laterally (from the pharynx to the tympanum), greatly facilitate the introduction of a Eustachian catheter.
The exact position of the orifice is of importance. It is situated on the side wall of the pars nasalis, a short distance (about to inch) behind the posterior end of the inferior concha, and immediately above the level of the hard palate (Figs. 902 and 903).
A slight ridge of the mucous membrane descends from the inferior end of the torus tubarius on the side wall of the pharynx, and gradually becomes lost. This is known as the plica salpingopharyngea. Another less-developed ridge, the plica salpingopalatina, passes from the anterior border of the ostium pharyngeum downwards and forwards to join the palate. In front of the latter lies the indistinct groove, the naso-pharyngeal groove, which indicates the separation of the nasal cavity from the nasal part of the pharynx.
The levator veli palatini in descending runs parallel to the tuba auditiva, and along its lower border. As it enters the palate, it produces, particularly when in a state of contraction, an elevation just below the pharyngeal orifice of the tube, known as the torus levatorius (Figs. 902 and 903), which in its upper portion abuts against the lower part of the orifice, and forms its base when that opening assumes its usual triangular shape.
Occasionally the osteum pharyngeum is of an oval or slit-like form, with sloping edges, but the triangular shape described above is much more commonly found.
Immediately posterior to each osteum pharyngeum is seen the recessus pharyngeus (O.T. lateral recess of the pharynx or fossa of Rosenmüller), a nearly vertical depression of considerable depth (Figs. 903 and 905), which extends laterally in the form of a flattened pouch or diverticulum.
FIG. 903. SAGITTAL SECTION THROUGH MOUTH, TONGUE, LARYNX, PHARYNX, AND NASAL CAVITY. The section is slightly oblique, and the posterior edge of the nasal septum has been preserved. The specimen is viewed slightly from below, hence, in part, the low position of the inferior concha.
The pharyngeal recesses project laterally over the superior margin of the superior constrictor. below the petrous portion of the temporal bone, and correspond in position to the sinus of Morgagni on each side (cf. description of pharyngeal wall, p. 1149). The recess has been considered to be the remains of the inner or pharyngeal portion of the second visceral cleft, the lower part of which is represented in the supra-tonsillar fossa, but more probably it is not connected with any of the visceral clefts, but makes its appearance after they have disappeared.
Pars Oralis.-The oral part of the pharynx lies behind the mouth, between the soft palate above and the superior aperture of the larynx below. On its anterior aspect is the isthmus of the fauces, leading into the mouth. Below this the vertical pharyngeal portion of the tongue forms the anterior wall.
Its side wall
(Fig. 903) presents a triangular area, sinus tonsillaris, bounded anteriorly by the glosso-palatine arch, posteriorly by the pharyngo-palatine arch, and below by the side of the tongue in its pharyngeal portion. This area is occupied in the greater part of its extent by the tonsil. Above the tonsil there is a depression, the fossa supratonsillaris (Fig. 903), which is of considerable clinical interest.
The arcus pharyngopalatinus (O.T. posterior pillar of the fauces) is a prominent fold of mucous membrane, containing in its interior the pharyngopalatinus muscle. It springs from the posterior edge of the soft palate, and, passing downwards and slightly backwards, ends inferiorly on the side wall of the pharynx (Fig. 903). The two pharyngo-palatine arches form the right and left boundaries of the pharyngonasal isthmus, and the orifice can be
modified in size by the contraction of the pharyngo-palatine muscles.
The arcus glossopalatinus is described on p. 1111.
The isthmus pharyngonasalis is the very oblique and somewhat triangular orifice through which the oral part communicates with the nasal part of the pharynx (Fig. 904). It differs considerably in size and shape in different individuals, being in some so small that the nasal part can be explored from the mouth only with very great difficulty; whilst in others it is of much larger dimensions (Fig. 905) and affords ample space for the rhinoscopic examination of the nasal part of the pharynx and the posterior part of the nasal cavities.
In general, it may be described
Pharyngopalatine arch Pharyngonasal isthmus
as triangular in shape, the sides corre- FIG. 904.-OPEN MOUTH SHOWING PALATE AND PALATINE sponding to the pharyngo-palatine
nasal isthmus, through which the nasal part, above, communicates with the oral part of the pharynx, below.
arches, and the base, which is behind, It also shows the two palatine arches, and the pharyngobeing formed by the posterior wall of the pharynx. The apex of the triangle
is directed towards the soft palate, and is encroached upon, and overlapped from below by the uvula, which assists in the closure of the orifice (Fig. 902).
By the contraction of the pharyngo-palatine muscles, which are enclosed within the pharyngo-palatine arches, the sides of the isthmus can be approximated, like two curtains, and its size correspondingly diminished. When, at the same time, the uvula and soft palate are elevated, and the whole pharynx in this region is narrowed by the contraction of the superior constrictor, the aperture can be completely closed, and the oral separated from the nasal part of the pharynx, as in the acts of swallowing and vomiting.
Tonsilla Palatina. The palatine tonsils are two large, oval masses of lymph tissue which are embedded in the side walls of the oral part of the pharynx, between the glosso-palatine and pharyngo-palatine arches (Fig. 904). As already pointed out, there is in this region a triangular interval (the sinus tonsillaris). The greater part of this interval is occupied by the tonsil. In its superior part, however, above the tonsil, there is usually found a variably developed depression already referred to as the fossa supratonsillaris.
The tonsillar sinus is bounded anteriorly by the glosso-palatine arch, passing from the inferior surface of the soft palate to the side of the tongue. Posteriorly it is bounded by the more vertical pharyngo-palatine arch, passing from the margin of the uvula to the side wall of the pharynx. The inferior boundary is formed by the margin of the tongue, while the narrow apex above passes up to the side of the soft palate. The tonsil occupies the inferior part of this sinus.