The pharynx is a fibromuscular tube, attached above to the base of the skull and continuous below with the oesophagus. It is about 12 cm in length. Its anterior wall is largely deficient and it thereby communicates with the nose, mouth and larynx. On account of these communications it is descriptively divided into three parts: nasal, oral and laryngeal, i.e. nasopharynx, oropharynx and laryngopharynx.
Muscles and fascia
The muscular wall is surprisingly thin. It consists of three curved sheets of muscle, the superior, middle and inferior constrictors (supplemented by three smaller muscles: stylopharyngeus, palatopharyngeus and salpingopharyn-geus). They overlap posteriorly, being telescoped into each other like three stacked cups. But the muscle does not extend up to the base of the skull; here the immobile wall of the nasopharynx consists of a rigid membrane, the pharyngobasilar fascia. This is a fibrous thickening of the submucosa that fills in the gap between the skull and the upper border of the superior constrictor, making a fourth but fibrous cup stacked inside the other three. The attachment of this fascia to the base of the skull (Fig. 6.35) can be traced from the pharyngeal tubercle, a midline thickening, in front of the foramen magnum, to which the pharyngeal raphe is attached (see below).
The attachment then passes laterally, convex forwards over longus capitis to the petrous part of the temporal bone just in front of the carotid canal. From here it passes forwards and medially below the cartilaginous part of the auditory tube, to the sharp posterior border of the medial pterygoid plate, along which it continues down to the hamulus. Suspended from the base of the skull, and sweeping around from one medial pterygoid plate to the other, the pharyngobasilar fascia holds the nasopharynx permanently open for breathing. As it descends inside the superior constrictor it diminishes in thickness and peters out below the level of the hard palate.
The quadrangular area at the apex of the petrous bone in front of the carotid canal lies within a lateral recess of the pharynx. The levator palati muscle arises here and is intrapharyngeal, covered medially by mucous membrane. The cartilaginous part of the auditory tube enters the nasopharynx above the pharyngobasilar fascia, which is firmly attached to its lower surface.
Superior constrictor
The superior constrictor fibres arise from the lower part of the posterior border of the medial pterygoid plate down to the tip of the hamulus, outside the pharyngobasilar fascia, and from the pterygomandibular raphe, which runs from the hamulus to the mandible just above the posterior end of the mylohyoid line. The superior constrictor passes backwards from the pterygomandibular raphe;
buccinator passes forwards from it (Fig. 6.13).
From its origins the muscle sweeps around the pharynx, its fibres diverging mostly upwards to meet their opposite fellows in the midline pharyngeal raphe (Fig. 6.36) at the back. The upper end of this raphe forms a fibrous band which receives the uppermost constrictor fibres and is attached to the pharyngeal tubercle. The lowest fibres extend at the back as far down as the level of the vocal folds, lying within the middle constrictor.
Figure 6.36 Pharynx, from behind. On the right the inferior constrictor has been removed to show the extent of the middle constrictor and the attachment of stylopharyngeus to the posterior border of the thyroid lamina.
There is a gap laterally between the superior and middle constrictors, through which stylopharyngeus passes down into the pharynx, and styloglossus and the glossopharyngeal and lingual nerves pass forwards to the tongue (Fig. 6.24).
Middle constrictor
The middle constrictor arises from the lower part of the stylohyoid ligament, the lesser horn of the hyoid bone and the greater horn, deep to hyoglossus. Its fibres diverge upwards and downwards as they sweep backwards around the pharynx to enclose the superior constrictor and end in the median raphe and the lowest fibres arch down as far as the vocal folds, lying within the inferior constrictor.
The anterior gap between the middle and inferior constrictors is closed by the thyrohyoid membrane (see p. 392), which thereby contributes to the wall of the laryngeal part of the pharynx (Fig. 6.37).
Passing through this gap by piercing the membrane are the internal laryngeal nerve and superior laryngeal vessels.
Figure 6.37 Pharyngeal constrictors, from the right.
Inferior constrictor
This has two parts, named from their origins. The thyropharyngeus part arises from the oblique line of the thyroid cartilage and in continuity below this from a fibrous arch that spans the cricothyroid muscle (Fig. 6.37). It encloses the middle and superior constrictors as its fibres curve backwards and upwards around them to the midline raphe. The cricopharyngeus, rounded and thicker than the flat sheets of the other constrictors, extends uninterruptedly from one side of the cricoid arch to the other around the pharynx. There is no raphe here. The muscle acts as a sphincter at the lower extent of the pharynx, and is continuous with the circular muscular coat of the oesophagus (Fig. 6.41). It is composed largely of fibres of the ‘slow twitch’ variety and is always closed, except for momentary relaxation during deglutition. It imparts some resistance to the passage of an endoscope (overcome by swallowing). The closure of the cricopharyngeus prevents air from being sucked into the upper oesophagus when intrathoracic pressure falls; air is sucked only into the permanently open trachea.
Passing upwards deep to the lower border of the inferior constrictor are the recurrent laryngeal nerve and inferior laryngeal vessels.
The junction between the oblique fibres of thyropharyngeus and the horizontal fibres of cricopharyngeus near the midline is a potentially weak area at the back of the pharyngeal wall (Fig.
6.36), and through this area (Killian's dehiscence) a pouch of mucosa may become protruded (pharyngeal diverticulum) (Fig. 6.38). Inappropriate contraction of cricopharyngeus during swallowing is an aetiological factor and surgical management includes division of its horizontal fibres.
Figure 6.38 Barium meal radiograph of a subject with a pharyngeal pouch. A residual film of barium sulphate has outlined the posterior surface of the tongue, the median and lateral glossoepiglottic folds and the piriform fossae.
Palatopharyngeus
Palatopharyngeus is described with the soft palate (see p. 389). As the muscle fibres pass down from the palate they lie internal to the superior constrictor (Fig. 6.41).
Salpingopharyngeus
Salpingopharyngeus is a very slender muscle that arises from the lower part of the cartilage of the auditory tube (see p. 416) and runs downwards (Fig. 6.41) to blend with palatopharyngeus.
Stylopharyngeus
Stylopharyngeus arises from the deep aspect of the styloid process high up. It slopes down across the internal carotid artery (Fig. 6.23), in front of which it crosses the lower border of the superior constrictor and passes down inside the middle constrictor, to be inserted with palatopharyngeus into the posterior border of the thyroid lamina (Fig. 6.36). The glossopharyngeal nerve curls round the posterior border of the muscle from medial to lateral, and supplies it.
Blood supply
Branches of many arteries supply the pharynx: ascending pharyngeal, ascending palatine and tonsillar (from facial), greater palatine and pharyngeal (from maxillary), lingual and the superior and inferior laryngeal arteries. Venous blood is largely collected into the pharyngeal venous plexus which like the nerve plexus (see below) is situated mainly at the back of the middle constrictor; it drains into the internal jugular vein and has connections with the pterygoid plexus.
Lymph drainage
Lymph passes to retropharyngeal lymph nodes and via these or directly to upper and lower deep cervical groups.
Nerve supply
The main motor nerve supply of the muscles of the pharynx is from the pharyngeal plexus. However, stylopharyngeus is supplied by the glossopharyngeal nerve and cricopharyngeus is also supplied by the recurrent and external laryngeal nerves. The cell bodies that supply all six muscles on each side are in the nucleus ambiguus.
The pharyngeal plexus lies on the posterolateral wall of the pharynx, mainly over the middle constrictor, and is formed by the union of pharyngeal branches from the vagus and glossopharyngeal nerves and the cervical sympathetic. The glossopharyngeal component is afferent; the pharyngeal fibres of the vagus carry motor fibres (derived from the cranial part of the accessory nerve). The sympathetic fibres are vasoconstrictor.
The mucosa of the nasopharynx is supplied by the pharyngeal branch of the maxillary nerve through the pterygopalatine ganglion. Most of the oropharynx receives its sensory supply from the glossopharyngeal nerve, but the internal laryngeal nerve supplies the valleculae and the lesser palatine nerves (maxillary) contribute to the supply of the tonsillar mucosa. The internal laryngeal nerve is sensory to the laryngopharynx.
Nasal part
The nasopharynx extends from the base of the skull to the upper surface of the soft palate, at the level of C1 vertebra. In front it communicates with the nose through the choanae. The space between the soft palate and the posterior pharyngeal wall through which the nasopharynx joins the oral part of the pharynx is the oropharyngeal isthmus. The soft palate becomes elevated during swallowing to meet
the posterior wall, so closing the isthmus. The main features within the nasopharynx are the openings of the auditory tubes, the pharyngeal recesses and the pharyngeal tonsil (Fig. 6.39)
Figure 6.39 Sagittal section of the head.
The opening of the auditory tube lies in the lateral wall and is triangular in appearance. The opening is guarded above, behind and in front by a prominent rounded ridge, the tubal elevation, formed by the trumpet-shaped medial end of the tubal cartilage as it underlies the mucous membrane, which here contains lymphatic tissue, the tubal tonsil. The tubal elevation is in the shape of an inverted J, the long limb lying posteriorly and being continued downwards as the salpingopharyngeal fold, produced by the underlying salpingopharyngeus muscle. The lower margin of the opening has a slight bulge due to the underlying levator palati muscle.
The pharyngeal recess (fossa of Rosenmüller) is a narrow vertical gutter behind the opening of the auditory tube, resulting from the angular attachment of the pharyngobasilar fascia to the base of the skull in front of the carotid canal (Fig. 6.35). A catheter missing the tubal orifice and introduced into the recess may perforate the fascia and enter the internal carotid artery, which here lies against the wall of the pharynx.
In the mucous membrane high on the posterior wall is a collection of lymphoid nodules, prominent only in chil-dren and forming the pharyngeal tonsil. When enlarged the nodules are commonly known as the adenoids.
Oral part
The oropharynx extends from the lower surface of the soft palate to the upper border of the epiglottis (halfway down C3 vertebral body). The wall of the oropharynx is formed posteriorly by all three constrictors. It closes completely behind a swallowed bolus, but is otherwise open for breathing.
Anteriorly in front of the gap between the soft palate and epiglottis there is a mobile wall, the posterior part of the tongue, above which the oropharynx communicates with the mouth. At the sides there are projecting ridges, the palatopharyngeal and palatoglossal arches (pillars of the fauces), formed by the underlying corresponding muscles, with the palatine tonsils between them. The palatoglossal arches form the boundary between the pharynx and the mouth. The palatine and lingual tonsils and the valleculae are in the oropharynx.
The palatine tonsil (the pair commonly called simply ‘the tonsils’) is a large collection of lymphoid
tissue which projects into the oropharynx from the tonsillar fossa between the palatopharyngeal fold behind and the palatoglossal fold in front (Fig. 6.33). The floor of the fossa (lateral wall) is the lower part of the superior constrictor. On its lateral aspect the glossopharyngeal nerve crosses the lower part of the bed, running obliquely downwards and forwards to reach the tongue by passing under the lower border of the constrictor.
The lymphoid tissue of the tonsil extends up to the soft palate and down to the dorsum of the tongue.
The medial surface is covered by pharyngeal mucosa on which are the openings of several epithelial downgrowths, the tonsillar crypts. One large downgrowth near the upper pole is the intratonsillar cleft, which is the remains of the fetal second pharyngeal pouch (see p. 26). The lateral surface is covered by fibrous tissue which forms the tonsillar hemicapsule. (A peritonsillar abscess occurs outside the capsule.) The superior constrictor separates this surface from the facial artery and two of its branches, the ascending palatine and tonsillar. The internal carotid artery is about 2.5 cm posterolateral to the tonsil.
The palatine, lingual, pharyngeal and tubal tonsils collectively form an interrupted circle of lymphoid tissue (Waldeyer's ring) at the upper end of the respiratory and alimentary tracts.
Blood supply. The tonsillar branch of the facial artery forms the main arterial supply; it enters the tonsil by piercing the superior constrictor. There are smaller contributions from the lingual, ascending pharyngeal and ascending and greater palatine vessels.
The veins form a plexus round the capsule and pierce the superior constrictor to drain into the pharyngeal plexus. One large vein descends from the soft palate between the tonsillar hemicapsule and the superior constrictor before piercing the pharyngeal wall; this is the external palatine, or paratonsillar vein and, is the usual cause of haemorrhage after tonsillectomy.
Lymph drainage. Lymphatic channels pierce the superior constrictor to reach the deep cervical nodes, especially the jugulodigastric (or tonsillar) node below the angle of the mandible.
Nerve supply. The mucous membrane overlying the tonsil is supplied mainly by the tonsillar branch of the glossopharyngeal nerve, and to a small extent by the lesser palatine nerves. The glossopharyngeal nerve also supplies the middle ear, through its tympanic branch, and tonsillitis may cause referred pain in the ear.
The valleculae lie between the epiglottis and the posterior surface of the tongue. They are shallow fossae separated by the median glossoepiglottic fold and limited inferolaterally by the lateral glossoepiglottic folds (Fig. 6.38). The nerve supply of the mucosa of the valleculae, including that of the part of the tongue that forms the anterior vallecular wall, is by the internal laryngeal nerve. A crumb that ‘goes down the wrong way’ is one that lodges in the vallecula and sets up a reflex bout of coughing (see p. 395) to dislodge it.
Laryngeal part
The laryngopharynx extends from the upper border of the epiglottis to the level of the lower border of the cricoid cartilage (C6 vertebra) where it becomes continuous with the oesophagus. In the upper part of the anterior aspect is the opening into the larynx (aditus or laryngeal inlet) (see p. 393). The piriform recesses, broad above and narrow below, lie beside the aperture of the larynx. Below the
inlet, the lower part of the pharynx (referred to clinically as the hypopharynx) possesses an anterior wall, comprising the arytenoids and the lamina of the cricoid cartilage (see p. 391) draped over with mucous membrane. The posterior wall of the laryngopharynx is formed by the three overlapping constrictors down to the level of the vocal folds (upper border of cricoid lamina). Below this (i.e.
behind the cricoid lamina) there is only the thyropharyngeus, the site of the dehiscence of Killian, and finally the cricopharyngeal sphincter.
At each side of the epiglottis the lateral glossoepiglottic fold separates the oropharynx from the laryngeal part. Below the fold is the piriform recess (piriform fossa) (Fig. 6.38). This mucosa-lined space is bounded medially by the quadrangular membrane of the larynx, (see p. 392), and laterally by the thyrohyoid membrane above and the lamina of the thyroid cartilage below (Fig. 6.40). A malignancy may grow in the space provided by the piriform fossa without producing symptoms, until the patient presents with metastatic cervical lymphadenopathy. The recesses are danger sites for perforation by an endoscope.
Figure 6.40 Laryngeal part of the pharynx from behind. On the right the mucous membrane has been removed to show the anastomoses within the pharynx of the superior and inferior laryngeal vessels and of the internal and recurrent laryngeal nerves. There is no such overlap in the larynx; the vocal folds are a complete ‘watershed’.
Soft palate
The soft palate hangs down from the back of the hard palate as a mobile flap that fuses at the sides of its anterior part with the lateral wall of the pharynx and which can be raised so that the posterior part of its superior surface makes contact with the posterior wall of the pharynx to close off the nasopharynx during swallowing. It consists of an aponeurosis that is acted upon by attached muscles to alter its shape and position, but much of its bulk is due to mucous and serous glands. There are five paired muscles: tensor palati, levator palati, palatoglossus (which also belongs to the tongue), palatopharyngeus (which also belongs to the pharynx) and the muscle of the uvula. The tensor and levator are properly called tensor veli palatini and levator veli palatini, but the older and simpler
name is retained here.
Tensor palati
This muscle arises outside the palate from the scaphoid fossa at the upper end of the medial pterygoid plate, the lateral side of the cartilaginous part of the auditory tube, and the spine of the sphenoid (Figs 6.19 and 6.35). From this origin the triangular muscle passes down between the medial and lateral pterygoid plates converging to a tendon that turns medially around the pterygoid hamulus, above the fibrous arch in the origin of the buccinator (Fig. 6.13), and so gets inside the pharynx. As to whether the tendon now is attached to the palatine aponeurosis, or flattens to become the fibrous aponeurosis, is academic. The triangular aponeurosis is attached anteriorly to the inferior surface of the hard palate behind the crest of the palatine bone (Fig. 6.35). The posterolateral borders of the aponeurosis blend with the side wall of the pharynx in front, but hang free behind, forming the edge of the soft palate and meeting at the dependent uvula in the midline. The aponeurosis is not flat, but concave towards the mouth; when tensed by contraction of the tensor muscle it is flattened and therefore depressed somewhat. The increased rigidity, however, enables the levator palati to elevate the soft palate during swallowing. The main action of the tensor palati is to tense the palatine aponeurosis so that other muscles may elevate and depress it without altering its shape. When the tensor palati contracts (e.g. in swallowing and yawning) it pulls upon the cartilage of the auditory tube, opens the tube, and permits equalization of air pressure between the middle ear and nose. This action is impaired in children with cleft palate, who hence have a higher incidence of middle ear problems.
Levator palati
This muscle arises from the quadrate area on the inferior surface of the apex of the petrous bone anterior to the carotid canal and from the adjacent medial side of the cartilaginous part of the auditory tube, it forms a rounded belly that is inserted into the nasal surface of the palatine aponeurosis between the two heads of palatopharyngeus. The two levator muscles in passing down to the palate are directed forwards and medially, together forming a V-shaped sling. Their contraction pulls the palate upwards and backwards. Contraction of the levator also opens the cartilaginous tube and equalizes air pressure between the middle ear and the nose.
Palatoglossus
The muscle arises from the undersurface of the palatine aponeurosis and passes downwards to interdigitate with styloglossus. The muscle raises the palatoglossal fold of mucous membrane in front of the tonsil (the anterior pillar of the fauces), marking the junction between mouth and pharynx. Its action is sphincteric at the oropharyngeal isthmus; it raises the tongue and reduces the transverse diameter of the isthmus.
Palatopharyngeus
The muscle arises from two heads. The anterior head arises from the posterior border of the hard palate and the anterior part of the upper surface of the palatine aponeurosis (Fig. 6.42). The posterior head arises further back on the upper surface of the aponeurosis. The two heads arch downwards over the lateral edge of the aponeurosis, join, and form a muscle that passes downwards beneath the mucous membrane and submucosa of the lateral wall of the pharynx just behind the tonsil (Figs 6.41 and 6.42). The upper part of the muscle raises the palatopharyngeal fold of mucous membrane that constitutes the posterior pillar of the fauces; the lower part (blending with stylopharyngeus and