The pharynx is a vertical, tubular passage, flattened anteroposteriorly, and extending from the base of the cranium above to the beginning of the esophagus below. Posteriorly, it is in contact with the bodies of the upper six cervical vertebrae.

Laterally, it is in relation with the internal and common carotid arteries, the internal jugular vein, the sympathetic and the last four cranial nerves.Anteriorly, it communicates above with the nasal cavity, beneath this with the oral cavity, and below with the laryngeal cavity. The pharynx is correspondingly divided into three parts: the nasal-pharynx [pars nasalis], which is exclusively respiratory in function; the oral pharynx [pars oralis], which is both respiratory and alimentary; and the laryngeal pharynx [pars laryngea], which is almost entirely alimentary.

Size and form

The average length of the pharynx is about 12 cm. (5 inches). It is widest at the nasal pharynx, with a constriction (isthmus) connecting it with the widened oral pharynx and is again somewhat narrowed at the junction of oral and laryngeal pharynx. It is narrowest at the point where it joins the esophagus below. In a sagittal section, it is evident that the anterior and posterior walls are closely approximated in the laryngeal pharynx and have only a small space between them in the oral pharynx. The nasal pharynx, however, has a considerable antero-posterior depth, and by its bony walls is always kept open for respiratory purposes.

Structure

The pharynx approaches the typical structure of the alimentary canal yet differs from it in several important respects. The lining mucosa is continuous with that of the various cavities which open into the pharynx. Above, it is closely adherent to the base of the cranium, where it is thick and dark in color. It becomes thinner where it approaches the openings of the auditory tubes and choanae; and below it is paler and thrown into longitudinal folds. The epithelium of the greater part of the nasal pharynx (from the orifice of the auditory tube upward) is stratified ciliated columnar, while that of the remainder of the pharynx is stratified squamous.

External to the mucosa, there is a characteristic fibrous membrane, the pharyngeal aponeurosis [fascia pharyngobasilaris], which is well marked above, but below it loses its density and gradually disappears as a definite structure. Above, it is attached to the basilar portion of the occipital bone in front of the pharyngeal tubercle. Its attachment may be traced to the apex of the petrous portion of the temporal bone, and thence to the auditory (Eustachian) tube and medial lamina of the pterygoid process. It descends along the pterygo-mandibular ligament to the posterior end of the mylohyoid ridge of the lower jaw and passes thence along the side of the tongue to the stylohyoid ligament, the hyoid bone, and thyroid cartilage.

External to the pharyngeal aponeurosis is a thick, muscular layer, made up of various cross-striated muscles, as will be described later. Outside of the muscular layer is a thin fibrous tunica adventitia, connected with the adjacent prevertebral fascia by a loose, areolar tissue. This loose tissue allows movement of the pharynx, and also favors the spreading of post- pharyngeal abscesses.

The nasal pharynx belongs, strictly speaking, with the nasal fossa as a part of the respiratory rather than the digestive system. Its anterior wall is occupied by the two choanae (posterior nares), with the nasal septum between them. The floor is formed by the upper surface of the soft palate and in a direct posterior continuation of the floor of the nasal fossae. Posteriorly, however, the floor presents a more or less narrowed opening, the pharyngeal isthmus, which communicates with the oral pharynx below. The isthmus is formed anteriorly by the uvula, laterally by the posterior (pharyngo-palatine) arches. These slope backward and downward to the posterior wall of the pharynx, which forms the posterior boundary of the isthmus. The floor and isthmus change their form and position greatly during the action of the palatal muscles, as will be mentioned later.

The lateral wall of the nasal pharynx presents above and behind, corresponding to its widest point, a wide, slit-like lateral extension, the pharyngeal recess [recessus pharyngeus] or fossa of Rosenmueller. Below and in front of this recess, the greater part of the lateral wall is occupied by the aperture of the auditory (Eustachian) tube [ostium pharyngeum tubae]. This is a somewhat triangular, funnel-shaped opening, with an inconspicuous anterior lip [labium anterius], a more distinct posterior lip [labium posterius], which presents posteriorly a rounded prominence (due to the projecting cartilage of the auditory tube), called the torus tubarius. The prominence of the posterior lip facilitates the intro- duction of the Eustachian catheter, in connection with which the location of the aperture in the mid-lateral wall just above the level of the floor of the nasal fossa should be carefully noted. On the lower aspect of the triangular apertm-e is a slightly rounded fold, the levator cushion, which is a prominence caused by the levator palati muscle. A fold of mucosa descending from the posterior lip of the aperture to the lateral pharyngeal wall is the plica salpingo-pharyngea (due to the m. salpingo-pharyngeus). An inconspicuous plica salpingo-palatina descends from the anterior lip to the soft palate.

The posterior wall of the nasal pharynx slopes from below upward and forward, passing (at the level of the anterior arch of the atlas) into the roof [fornix pharyngis]. The roof is attached chiefly to the basi-occipital and basi-sphenoid bones, extending laterally to the carotid canal of the pyramid, and anteriorly to the base of the nasal septum. In the posterior wall of the nasal pharynx, there is found in the mucosa a variable and inconstant blind sac, the pharyngeal bursa.

The mucosa of the roof, and to a certain extent also of the posterior wall, especially in children, is thrown into numerous folds, which may be irregular or radiate from the neighborhood of the bursa. There is often a median longitudinal groove (or sometimes ridge) at the posterior (inferior) end of which is the bursa. These folds of the mucosa contain much lymphoid tissue, both diffuse and in the form of numerous characteristic lymphoid nodules, with crypt-like invaginations of the surface epithelium. This area constitutes the pharyngeal tonsil [tonsilla pharyngea], which is well-developed in children (often abnormally enlarged, producing 'adenoids'), but usually, though not always, atrophied in the adult. According to Symington, the involution of the pharyngeal tonsils begins at 6 or 7 years and is usually completed at 10 years. In the region of the pharyngeal tonsil and elsewhere, the mucosa presents numerous small racemose mucous glands, especially thick in the palatal floor of the nasal pharynx and similar to those of the oral cavity.

The oral pharynx is continuous above through the pharyngeal isthmus with the nasal pharynx and below with the laryngeal pharynx. Its posterior wall presents no special features. 

Vertical Section of a Human Palatine Tonsil,

a, Stratified epithelium; b, basement membrane; c, tunica propria; d, trabeculse; e, diffuse lymphoid tissue; /, nodules; h, capsule; i, mucous glands; k, striated muscle; l, blood vessel; q, pits. (From Radasch.)

 

 

The anterior wall is deficient above, where there is a communication with the mouth cavity through the isthmus faucium. The faucial isthmus is bounded above by the uvula, laterally by the anterior (glosso-palatine) arches, and below by the dorsum of the tongue in the region of the sulcus terminalis. Below the faucial isthmus, the anterior wall of the oral pharynx is formed by the root of the tongue, which has been described previously. The lateral wall of the oral pharynx on each side presents the palatine tonsil, enclosed in a somewhat triangular tonsillar fossa [sinus tonsillaris] limited anteriorly and posteriorly by the anterior and posterior palatine arches, and below by the root of the tongue.

The palatine arches are folds of the mucosa formed at the sides of the free posterior border of the soft palate, as already mentioned in connection with that organ. The anterior arch (or pillar) [arcus glossopalatinus] extends from the soft palate downward and forward to the lateral margin of the tongue, just behind the papillae foliatae. It is a fold of mucosa due to the underlying glosso-palatine muscle, and inconspicuous except when this muscle is in action, or when the tongue is depressed. It forms the lateral boundary of the faucial isthmus. The posterior arch [arcus pharyngopalatinus] is a more prominent fold which extends from the soft palate in the region of the uvula downward and backward to join the postero-lateral aspect of the pharyngeal wall. It forms the lateral boundary of the pharyngeal isthmus and encloses the pharyngo-palatine muscle, whose action will be explained later.

The palatine tonsil [tonsilla palatina] is a flattened ovoidal body, usually visible through the mouth cavity and faucial isthmus, and located on each side of the oral pharynx. The tonsil is extremely variable in size, but in the young adult averages about 20 mm. in height, 15 mm. in width (anteroposteriorly) and 12 mm. in thickness.

The lateral or attached surface of the tonsil is covered by a thin but firm fibrous capsule, which is continuous with the pharyngeal aponeurosis, and in contact with the middle constrictor muscle of the pharynx. Just outside the constrictor, the tonsil is in relation with the ascending pharyngeal and ascending palatine arteries but is separated by a considerable space from the external and internal carotids. Rarely, however, the lingual or external maxillary may extend up higher than usual, so as to be in close relation with the lower aspect of the tonsil. Further lateralward, the palatine tonsil is in relation with the internal pterygoid muscle, and on the surface corresponds to a point somewhat above and in front of the angle of the mandible. The posterior border of the tonsil is thicker than the anterior and forms a somewhat flattened surface in contact with the pharyngo-palatine muscle.

The medial or free surface of the tonsil is covered with mucosa and presents a variable number (12 to 30) small pits which are the openings into the tubular or slit-like crypts [fossulae tonsillares]. These crypts are somewhat more numerous in the upper part of the tonsil and are sometimes branched or irregular in form. Usually, they end blindly in the substance of the tonsil, surrounded by lymphoid tissue in characteristic nodular masses. The lymphocytes normally migrate through the stratified squamous epithelium lining the crypts (occasionally eroding passages of considerable size), and escape into the pharyngeal and mouth cavities, where they form the so-called salivary corpuscles. Around the periphery of the palatine tonsil, within the capsule, are many mucous glands (fig. 889), similar to those described in connection with the lingual and pharyngeal tonsils. The ducts of the mucous glands sometimes enter the crypts, but usually pass to the surface chiefly around the margins of the palatine tonsil.

Tonsillar plicae and fossae

Connected with the tonsil are certain important folds and fossae. The plica triangularis is a fold of variable extent and appearance, placed just behind the anterior arch, wider below and narrower above. According to Fetterolf, it is a prolongation of the tonsillar capsule, covered with mucosa. It may be adherent to the anterior part of the medial surface of the tonsil, or it may be free, in which case it covers a recess called the anterior tonsillar fossa. Occasionally there is a similar plica and fossa at the posterior border of the tonsil. Above the tonsil there is similarly a supratonsillar fossa [fossa supratonsillaris], which is also inconstant and exceedingly variable in size and shape. Killian found a supratonsillar fossa or canal in 41 of 105 cadavers.

Tonsillar vessels

The arteries to the tonsil include the anterior tonsillar (from the dorsalis linguEe); the inferior tonsillar (from the external maxillary); the -posterior tonsillar (from the ascending pharyngeal) and the superior tonsillar (from the descending palatine). These pierce the capsule and supply the gland. The veins form a plexus around the capsule and empty into the lingual vein and the pharyngeal plexus. The lymphatic relations of the palatine tonsil are important. Afferent vessels are received from adjacent areas of the mucosa in the pharynx, mouth and lower part of the nasal cavity (v. Lenart). These are connected with an extensive lymphatic plexus around the lymph follicles within the tonsil. Efferent lymphatic vessels pass chiefly to the upper deep cervical lymphatic nodes. One of these, located just behind the angle of the mandible, is so closely connected with the tonsil, and so constantly enlarged following tonsillar infection, that it has been called the tonsillar lymph gland (Wood). There are also communications with the submaxillary and superficial cervical lymphatic nodes. The tonsillar lymphatic vessels connect also with those of the lingual tonsil in the root of the tongue.

The tonsillar ring

The two palatine tonsils, together with the lingual tonsil below and the pharyngeal tonsil above, form an almost complete ring of characteristic tonsillar tissue surrounding the pharynx and known as Waldeyer's 'tonsillar ring'. It is a highly specialized development of the diffuse lymphoid tissue which is found everywhere in the mucosa of the alimentary and respiratory tracts. It may be noted that the 'tonsillar ring' corresponds to the anterior limit of the embryonic foregut, hence the epithelium is of endodermic origin. The arrangement of the tonsils, together with their lymphatic connections, has suggested the widely accepted view that they are to be considered as protective mechanisms whose function is to intercept infectious material which has entered the mouth or nasal cavities. This theory is supported by the experiments of v. Lenart, who found that substances injected into the nasal mucosa are intercepted partly in the tonsils, and partly in the cervical lymph nodes. Oppel, however, opposes this view, holding that the function of the tonsils, as of lymphoid tissue elsewhere, is merely the production of lymphocytes.

The Left Palatine Tonsil, Showing the Arterial Supply.

1, Mesial aspect. 2, Postero-lateral aspect. E, lateral surface. B, posterior surface. T, medial surface. G, groove for pharyngo-palatine muscle. C, capsule. PT, plica triangularis. Arteries: AA, anterior tonsillar (from dorsal lingual); PA, posterior tonsillar (from ascending pharyngeal) ; SA, superior tonsillar (from descending palatine) ; lA, inferior tonsillar (anterior from dorsal lingual; posterior from tonsillar branch of internal maxillary). (Fet- terolf : Amer. J. Med. Sc, 1912.)

Development of the tonsil

According to Hammar, the palatine fossa (sinus tonsillaris) is a derivative of the second inner branchial groove and is visible in the human embryo of 17 mm. There appears in the floor of the fossa a tubercle (tuberculum tonsillare) which later becomes atrophied, excepting a portion which is converted into the plica triangularis. The primitive tonsil becomes divided into two lobes, upper and lower, by a fold (plica intratonsillaris) which later usually disappears. In the fetus of about 100 mm. (crown-rump length) the epithelium of the floor grows into the subjacent mesenchyme in the form of somewhat irregular solid sprouts of epithelium. These later become hollow and form the crypts. Around them, in about the sixth foetal month, the lymphoid tissue begins to accumulate, at first diffusely, later forming characteristic follicles. The lymphocytes arise in situ from the connective-tissue cells (Hammar) or by immigration from the blood-vessels (Stohr). Retterer's claim that the tonsillar lymphoid cells are derived from the epithelial cells has not been confirmed.

The later foetal development of the tonsil is subject to considerable individual variation. The supratonsillar fossa is a remnant of the upper part of the primitive sinus tonsillaris, which may be transformed into a canal by growth of adenoid tissue around it. It is inconstant and quite variable in size and extent. A portion of the sinus may likewise persist anteriorly (anterior tonsillar fossa) between the tonsil and the plica triangularis, but this portion is usually obliterated by fusion of the plica with the tonsil. The occasional retro-tonsillar fold and fossa are said to arise secondarily (Hammar).

Variations in the tonsil

The palatine tonsil, like the lingual and pharyngeal tonsils, is an exceedingly variable organ. Many of the variations are developmental in origin, as above indicated, and are therefore congenital. Furthermore, the tonsils, like all lymphoid structures, are subject to marked age variations. Though fairly well formed at birth, they are yet somewhat undeveloped. They rapidly increase in relative size and complexity, however, being best developed in childhood. After the age of puberty, they usually undergo certain retrogressive changes, become smaller in size, and in old age become almost entirely atrophied and lost. They are also markedly subject to inflammatory hypertrophy, especially in children. Variations in the relations of the blood-vessels were mentioned above.

The laryngeal pharynx is the lower portion leading from the oral pharynx above into the esophagus below (at the level of the lower border of the cricoid cartilage, usually opposite the sixth cervical centrum). It is wide above and narrow below. Its posterior walls are continuous with those of the oral pharynx and in relation with the vertebral centra. Its lateral walls are attached to the hyoid bone and the posterior part of the medial surface of the thyroid cartilage. Anteriorly it is in relation with the larynx. In the median line above is the epiglottis, below which is the superior aperture of the larynx. Still lower is the posterior wall of the larynx, containing the arytenoid and lamina of the cricoid cartilage. Laterally, are the pharyngo-epiglottic folds, and below these on each side a deep, elongated fossa, the recessus piriformis, bounded laterally by the medial surface of the thyroid cartilage. The mucosa of the laryngeal pharynx is similar to that of the oral pharynx and contains racemose mucous glands, which are especially numerous in its anterior wall.

Muscles of the pharynx and soft palate

These muscles, which are here grouped together for convenience of description, are chiefly sphincter-like constrictors in function. They include the constrictors of the faucial isthmus (mm. glossopalatini), the constrictors of the pharyngeal isthmus (mm. pharyngopalatini), the three pharyngeal constrictors and also the levator and the tensor veil palatini, the m. uvulae and the stylopharyngeus. The stylopharyngeus and pharyngo-palatine muscles form an incomplete longitudinal layer within the more circularly arranged constrictors of the pharynx.

The muscles are arranged in layers either behind or in front of the aponeurosis, and in a horizontal section of the soft palate the following layers are met with from behind forward: (1) The mucous membrane on the pharyngeal surface; (2) the posterior layer of the pharyngo-palatinus (palato-pharyngeus) ; (3) the m. uvulae; (4) the levator veli palatini; (5) the anterior layer of the pharyngo-palatinus; (6) the palatal aponeurosis with the tensor veli palatini; (7) the glosso-palatinus palato-glossus) ; and (8) the mucous membrane on the oral aspect.

The glosso-palatinus (palato-glossus)

It is a cylindrical muscle extending between the soft palate and the lateral border of the tongue.

Origin

- From the oral surface of the palatal aponeurosis.

Insertion

- (1) The superficial layer of muscles which covers the side and adjacent part of the under surface of the tongue; (2) the transversus linguae.

Structure

- At its origin the muscle forms a thin sheet, but the fibers, passing lateralward, quickly concentrate to form a cylindrical bundle, which passes downward beneath the mucous membrane of the pharynx and in front of the tonsil, forming the glosso-palatine arch of the fauces. It reaches the side of the tongue at the junction of its middle and posterior thirds, and some of its fibers continue forward to join with those of the stylo-glossus and hyo-glossus, while the majority pass medially to become continuous with the transversus linguae. Nerve-supply. - From the pharyngeal branches (plexus) of the vagus. Action. - (1) To draw the sides of the soft palate downward; (2) to draw the sides of the tongue upward and backward. The combination of these actions tends to constrict the faucial isthmus. (The origin and insertion of the glosso-palatinus as given above are often described as reversed.)

The pharyngo-palatinus (palato-pharyngeus)

- named from its attachments - is a thin sheet.

Origin

- (1) From the aponeurosis of the soft palate by two heads which are separated by the insertion of the levator veli palatini; (2) by one or two narrow bundles from the lower part of the cartilage of the auditory (Eustachian) tube (salpingo-pharyngeus) .

Insertion

- (1) By a narrow fasciculus into the posterior border of the thyreoid cartilage near the base of the superior cornu ; (2) by a broad expansion into the fibrous layer of the pharynx at its lower part .

Structure

The upper head of the muscle consists of scattered fibers which blend with the opposite muscle across the middle line; the lower head is thicker and follows the curve of the posterior border of the palate. The two heads with the fasciculus from the auditory (Eustachian) tube form a compact muscular band in the posterior palatine arch; the fibers mingle with those of the stylopharyngeus, at the lower border of the superior constrictor, and then expand upon the lower part of the pharynx. Nerve-supply. - From the pharyngeal branch (plexus) of the vagus. Action. - (1) Approximates the posterior arches of the fauces; (2) depresses the soft palate; (3) elevates the pharynx and larynx. (The origin and insertion above given are often described as reversed.)

The inferior constrictor is thick and strong. It arises from the thyreoid cartilage immediately behind the oblique hne and superior tubercle (thyropharyngeal), and from a tendinous arch extending between the inferior tubercle of the thyroid and the cricoid cartilage and also from the lateral surface of the cricoid cartilage (cricopharyngeal). The fibers spread backward and medialward, the lowest horizontally, whilst those above ascend more and more obliquely, and are inserted into the fibrous raph6 of the pharynx. Some of the lowest fibers are continuous with the muscular fibers of the esophagus, and the upper overlap the middle constrictor. The nerve-supply of all three constrictors is from the pharyngeal nerve.

Near the upper border the superior laryngeal nerve and artery pierce the thyreo-hyoid membrane to reach the larynx. The inferior laryngeal nerve ascends beneath the lower border immediately behind the crico-thyroid articulation.

The middle constrictor is a fan-shaped muscle which arises from the lesser cornu of the hyoid bone and from the stylo-hyoid ligament (chondro-pharyngeus), and from the whole length of the greater cornu (cerato-pharyngeus). The diverging fibers are inserted into the median raphe, and blend with those of the opposite side. The lower fibers of the muscle descend, beneath the inferior constrictor, to the lower part of the pharynx; the upper overlap the superior constrictor, and reach the basilar process of the occipital bone, whilst the middle fibers run transversely.

The glosso-pharyngeal nerve passes downward above its upper border, the stylopharyngeus passes between it and the superior constrictor, and near its origin it is overlapped by the hyo-glossus and crossed by the lingual artery.

The superior constrictor is quadrilateral in shape, pale, and thin. It arises from the lower third of the hinder edge of the median lamina of the pterygoid process and its hamular process (pterygo-pharyngeus), from the pterygo-mandibular ligament (buoco-pharyngeus), from the posterior fifth of the mylo-hyoid ridge of the mandible (mylo-pharyngeus), and from the side of the root of the tongue (glosso-pharyngeus). The fibers pass backward to be inserted into the median raphe, the highest reaching the pharyngeal tubercle. The Eustachian tube and the levator veli palatini are placed above the superior arched border, and the space {sinus of Morgagni) between this and the basilar process, devoid of muscular fibers, is strengthened by the pharyngeal aponeurosis, this portion of it being semilunar in shape.

The stylopharyngeus arises from the base of the styloid process internally. It passes downward and medialward to reach the pharynx between the superior and middle constrictors. Its fibers spread out as it descends beneath the mucous membrane. At the lower border of the superior constrictor some of its fibers join fibers of the pharyngo-palatinus (palato-pharyngeus), and are inserted into the posterior border of the thyroid cartilage; the rest blend with the constrictors. The nerve-supply of the stylopharyngeus is from the glosso-pharyngeal nerve.

The levator veli palatine

- named from its action on the velum of the soft palate - is some- what rounded in its upper, but flattened in its lower, half.

Origin.

- (1) The inferior surface of the petrous portion of the temporal, anterior to the orifice of the carotid canal; (2) the lower margin of the cartilage of the auditory (Eustachian) tube.

Insertion

The aponeurosis of the soft palate; the terminal fibers of the muscles of each side meet in the middle line in front of the m. uvulae.

Structure

Its origin is by a short tendon; the muscle then becomes fleshy and continues so to its insertion.

Nerve-supply

- From a pharyngeal branch (plexus) of the vagus.

Action

- (1) To raise up the velum of the soft palate and bring it in contact with the posterior wall of the pharynx; (2) to narrow the pharyngeal opening and to widen the isthmus of the auditory (Eustachian) tube. (According to Cleland, it closes the pharyngeal opening of this tube.)

The tensor veli palatine

named from its action on the velum of the soft palate - is a thin, flat, and narrow sheet.

Origin

. - (1)The scaphoid fossa of the sphenoid; (2) the angular spine of the sphenoid; (3) the lateral side of the membranous and cartilaginous wall of the auditory (Eustachian) tube.

Insertion

- (1) Into the transverse ridge on the under surface of the horizontal plate of the palate bone; (2) the aponeurosis of the soft palate.

Structure

Its belly as it descends between the pterygoideus internus and the internal pterygoid plate is muscular. On approaching the hamular process it becomes tendinous and continues so to its insertion. A bursa is interposed between the hamular process and the tendon. The belly of the muscle is at nearly a right angle with its tendon.

Nerve-supply. –

From the mandibular division of the trigeminus through the tensor palati branch of the otic ganglion.

Actions

- (1) Tightens the soft palate; (2) opens the auditory (Eustachian) tube during deglutition.

The m. uvulae

so named by reason of its position in the uvula. Origin. - (1) From the aponeurosis of the soft palate and tendinous expansions of the two tensores veli palatini. Insertion. - Into the uvula. Structure. - The muscle consists of two narrow parallel strips lying on each side of the middle line of the palate. Nerve-supply. - From the pharyngeal branch of the vagus. Action. - To draw up the uvula.

Origin of the muscles

According to W. H. Lewis, the tensor palati is a derivative of the mandibular arch (probably split off from the pterygoid mass); the levator palati and m. uvulae come with the facial musculature from the hyoid arch; the glosso-palatine, stylo-pharyngeus and pharyngeal constrictors probably from the third visceral arch, in a pre-muscle mass visible in a 9 mm. embryo. The adult innervation of the pharyngeal muscles does not agree entirely with this, however. The pharyngeal muscles (as above stated) are innervated chiefly from the vagus, whereas if derived from the third arch their innervation from the glosso-pharyngeus would be expected.

Process of swallowing

In the act of swallowing, practically all of the muscles of the mouth, tongue, palate and pharynx are involved. By compression of the lips and cheeks, together with elevation of the tongue, the food is forced backward through the faucial isthmus into the oral pharynx. Constriction of the faucial isthmus by the glosso-palatine muscles assists in preventing a return to the mouth. By the action of the levator palati, tensor palati, and pharyngo-palatine muscles, the soft palate is retracted and tightened, with constriction of the pharyngeal isthmus, so as to prevent the passage of the food upward into the nasal pharynx. The pharynx is drawn upward by the stylopharyngeus, and the pressure produced by the pharyngeal constrictors (the contraction beginning above and extending downward) forces the food downward through the laryngeal pharynx and into the esophagus. Passage of the food into the larynx is prevented by constriction of the superior aperture of the larynx.

Vessels and nerves

The vessels of the tonsil and the motor nerves of the various muscles have already been mentioned. In general, the arteries to the pharynx are derived chiefly from the ascending pharyngeal, the ascending palatine branch of the external maxillary, and the descending palatine and pterygo-palatine branches of the internal maxillary. The veins form a venous plexus between the pharyngeal constrictors and the pharyngeal aponeurosis, and also an external plexus, communicating with the pterygoid plexus above and with the posterior facial or internal jugular vein below. The lymphatic vessels pass chiefly to the deep cervical nodes, those from the upper portion (including the pharyngeal tonsil) ending partly in the retro-pharyngeal glands. The nerves of the pharynx, both motor and sensory, are derived chiefly from the glosso-pharyngeal and vagus, by way of the pharyngeal plexus.

The development of the pharynx

The pharynx is developed chiefly (if not entirely) from the anterior end of the archenteron. In this portion of the archenteron, with the development of the branchial arches, there are formed on each side four entodermal pouches or grooves (with a rudimentary fifth), the branchial clefts. With further development the first pair of branchial clefts form the tympanic cavities and the auditory or Eustachian tubes; the lower portion of each second branchial cleft persists as a fossa in which a palatine tonsil is developed; the remains of the third and fourth pairs are found on each side in the vaUecula and piriform sinus of the larynx. The origin of the pharyngeal tonsil may be observed in the  third month of foetal life in the form of small folds of mucous membrane which, during the sixth month, become infiltrated with diffuse adenoid tissue, lymph-nodules differentiating in this toward the end of fetal life. The pharyngeal bursa, which is not a constant structure (Kilrlian), may be observed as a small diverticulum of the pharyngeal wall, closely connected with the anterior extremity of the notochord. The diverticulum develops independently of Rathke's pouch (which gives rise to the anterior portion of the hypophysis) and is also apparently distinct from Seesel's pocket.

The entire pharynx, like the associated facial region, is relatively small and undeveloped in the fetus and newborn but develops rapidly during infancy. The development of the muscles and of the palatine tonsils has already been considered.

Variations

Variations in the palatine and pharyngeal tonsils and in the pharyngeal bursa have already been mentioned. Remnants of the visceral clefts may persist as aberrant diverticula or as 'branchial fistulae' connected with the pharynx. Many additional muscles have been described, chiefly longitudinal muscles arising from the base of the cranium either by splitting of those normally present, or as separate slips. A detailed description of these may be found in Poirier-Charpy's work. Abnormally extensive fusion of the posterior arches of the palate with the walls of the pharynx may produce a congenital stenosis of the pharyngeal isthmus.

Comparative

The pharynx is not distinctly separated from the mouth cavity in the lower vertebrates. It is the region containing the branchial or visceral clefts and is thus both respiratory and alimentary in function. The nasal pharynx, including the apertures of the auditory tubes, becomes distinct along with the nasal cavity when the palate is formed (from the reptiles upward). In the air-breathing vertebrates, the laryngeal aperture appears in the ventral wall of the pharynx just anterior to the beginning of the esophagus. Of the tonsils, the pharyngeal are the most primitive, being present in the roof of the pharynx in amphibia, well-developed in reptiles, birds, and mammals (Killian). The palatine tonsils, on the other hand, are characteristic of mammals, being rarely absent, however (e. g., rat, guinea pig). From the embryological point of view, Hammar has classified the palatine tonsils in the various mammals under (1) the primary type (including rabbit, cat, and dog), in which the tonsil is formed from the embryonic tonsillar tubercle (described above under development of tonsil); and (2) the secondary type (including pig, ox, sheep and man), in which the tonsillar tubercle disappears and the tonsil is developed from the wall of the surrounding tonsillar sinus. Typical epithelial crypts (highly branched in the ox) are found only in the secondary type. The tonsil may form a single (lymphoid) lobe (cat, pig, rabbit) or may develop typically two lobes (ox, sheep, man), separated by the intratonsillar fold. There are great variations among different species as to relative size, number and character of folds, crypts, etc. The intimate relation of the epithelium with the underlying lymphoid tissue is characteristic and constant.

Comments (0)

There are no comments posted here yet

Leave your comments

  1. Posting comment as a guest. Sign up or login to your account.
Attachments (0 / 3)
Share Your Location

This website puts documents at your disposal only and solely for information purposes. They can not in any way replace the consultation of a physician or the care provided by a qualified practitioner and should therefore never be interpreted as being able to do so.