# Lecture 11: Oral Cavity and Pharynx ## Unit 1.5: Human Gross Anatomy III - Pelvis and Head/Neck --- ## Learning Objectives By the end of this lecture, students will be able to: 1. Describe the boundaries and contents of the oral cavity 2. Describe the anatomy of the tongue and its innervation 3. Identify the salivary glands and their drainage 4. Describe the divisions of the pharynx and their contents 5. Explain the anatomy of the palate and tonsils 6. Correlate anatomical features with clinical conditions --- ## Oral Cavity Overview The oral cavity is the first portion of the alimentary tract and serves functions including ingestion, mastication, taste, and initiation of swallowing. It is divided into two regions by the dental arches. The vestibule is the slit-like space between the lips and cheeks externally and the teeth and gums internally. When the teeth are occluded, the vestibule communicates with the oral cavity proper only through the gap behind the last molar teeth. This fact is clinically important when feeding patients with jaw fixation. The oral cavity proper is the larger space enclosed by the dental arches, containing the tongue and receiving the ducts of the major salivary glands. The boundaries of the oral cavity proper are as follows: anteriorly and laterally, it is bounded by the teeth and alveolar ridges; superiorly, by the hard and soft palate; inferiorly, by the muscular floor of the mouth formed primarily by the mylohyoid muscles; and posteriorly, it communicates with the oropharynx through the oropharyngeal isthmus (also called the fauces). The oropharyngeal isthmus is bounded superiorly by the soft palate, laterally by the palatoglossal arches (the anterior pillars of the fauces), and inferiorly by the tongue. Panel A: Midsagittal section of the head showing the vestibule as the space between lips/cheeks and teeth. Panel B: Oral cavity proper within the dental arches bounded by hard and soft palate superiorly. Panel C: Tongue and floor of mouth inferiorly with the oropharyngeal isthmus (fauces) posteriorly connecting to the oropharynx. Panel D: Key structures labeled including uvula, palatoglossal arch, and epiglottis. --- ## Lips and Cheeks The lips are mobile muscular folds surrounding the oral orifice. Their external surface is covered by skin, and their internal surface by oral mucosa. The junction between these surfaces is the vermilion border, a zone of modified, highly vascularized skin that lacks sweat glands and sebaceous glands, accounting for the lips' characteristic red color and tendency to become chapped. The orbicularis oris muscle forms the sphincter of the oral orifice, and numerous other facial muscles insert into the lips to produce the varied movements of speech and expression. The superior and inferior labial arteries (branches of the facial artery) supply the upper and lower lips respectively, forming an arterial ring around the mouth. Sensory innervation is provided by the infraorbital nerve (V2) for the upper lip and the mental nerve (V3) for the lower lip. The cheeks form the lateral walls of the oral cavity and are composed primarily of the buccinator muscle, covered externally by skin and internally by oral mucosa. The buccinator maintains food between the teeth during mastication and assists in forceful exhalation (as when playing a wind instrument). Superficial to the buccinator lies the buccal fat pad, which is particularly prominent in infants and aids in suckling. The parotid duct (Stensen's duct) pierces the buccinator to open into the vestibule opposite the upper second molar. Sensory innervation of the cheek is provided by the buccal nerve from V3 (note that the buccal branch of the facial nerve supplies motor innervation to the buccinator, a common source of confusion). Panel A: Anterior view of the orbicularis oris forming the lip sphincter. Panel B: Buccinator muscle forming the cheek wall with the parotid duct piercing it. Panel C: Parotid duct opening marked at upper second molar level in the vestibule. Panel D: Blood supply showing labial arteries forming an anastomotic ring with sensory nerve territories indicated. --- ## Teeth and Gums The adult dentition comprises thirty-two permanent teeth: eight incisors, four canines, eight premolars, and twelve molars. The dental formula for each half of the jaw is 2-1-2-3 (two incisors, one canine, two premolars, three molars). The third molars (wisdom teeth) are the last to erupt and are frequently impacted. Each tooth consists of a crown (the portion visible above the gum line, covered by enamel), a neck (at the gum line), and one or more roots (embedded in the alveolar bone, covered by cementum). The bulk of the tooth is composed of dentin, which surrounds the central pulp cavity containing nerves, blood vessels, and connective tissue. The periodontal ligament anchors the root cementum to the alveolar bone. The blood supply to the upper teeth comes from the superior alveolar arteries: the posterior superior alveolar artery (a branch of the maxillary artery) supplies the molars and premolars, while the anterior superior alveolar artery (from the infraorbital artery) supplies the incisors and canines. The lower teeth receive blood from the inferior alveolar artery, a branch of the maxillary artery that enters the mandibular foramen and runs within the mandibular canal. Venous drainage parallels the arterial supply. Innervation of the upper teeth is provided by the superior alveolar nerves derived from V2: the posterior superior alveolar nerve supplies the molars (except the mesiobuccal root of the first molar), and the middle and anterior superior alveolar nerves supply the remaining teeth. The lower teeth are innervated by the inferior alveolar nerve from V3, which enters the mandibular canal and emerges partly as the mental nerve (supplying the lower lip and chin) and partly as the incisive nerve (continuing to supply the anterior teeth). The gingiva (gums) consists of attached gingiva firmly bound to the underlying alveolar bone and the free gingiva forming a collar around each tooth neck. Innervation of the gingiva mirrors that of the adjacent teeth. Panel A: Cross-section of a molar tooth showing crown covered by enamel and dentin forming the bulk of the tooth. Panel B: Central pulp cavity with neurovascular bundle and root covered by cementum. Panel C: Periodontal ligament and surrounding alveolar bone supporting the tooth. Panel D: Innervation patterns showing superior alveolar nerves (V2) for upper teeth and inferior alveolar nerve (V3) entering mandibular foramen for lower teeth. --- ## Tongue The tongue is a muscular organ essential for taste, speech, mastication, and swallowing. It occupies most of the oral cavity and is attached to the floor of the mouth and to the hyoid bone and mandible. The tongue is divided into two portions by the sulcus terminalis, a V-shaped groove on the dorsal surface with its apex pointing posteriorly toward the foramen cecum. The anterior two-thirds (oral part or body) lies within the oral cavity and is separated from the posterior one-third (pharyngeal part or root) by this groove. The foramen cecum marks the embryological origin of the thyroglossal duct and thus the site of origin of the thyroid gland. The undersurface of the tongue shows the lingual frenulum in the midline, with the deep lingual veins visible on either side. The dorsal surface of the anterior two-thirds is covered by lingual papillae of four types. Filiform papillae are the most numerous, cover the entire dorsum, have a mechanical function (providing roughness), and do not bear taste buds. Fungiform papillae are scattered among the filiform papillae, most numerous at the tip and edges, appear as red dots (due to their vascularity), and contain taste buds. Circumvallate (vallate) papillae number only eight to twelve, are arranged in a row just anterior to the sulcus terminalis, are the largest papillae, and are surrounded by trenches containing taste buds. Foliate papillae are rudimentary in humans, located at the posterolateral edges of the tongue, and contain taste buds. The posterior one-third of the tongue lacks papillae but features irregular nodules of lymphoid tissue constituting the lingual tonsil, part of Waldeyer's ring. Panel A: Superior view of the tongue dorsum showing the V-shaped sulcus terminalis dividing anterior two-thirds from posterior one-third with foramen cecum at its apex. Panel B: Filiform papillae covering the dorsum (tiny projections) and fungiform papillae as scattered red dots especially at the tip. Panel C: Large circumvallate papillae in a V-row anterior to the sulcus and foliate papillae on lateral edges. Panel D: Posterior third showing nodular lingual tonsil tissue. --- ## Muscles of the Tongue The musculature of the tongue consists of intrinsic muscles (confined to the tongue, altering its shape) and extrinsic muscles (with external attachments, moving the tongue as a whole). The intrinsic muscles are arranged in three planes. The superior longitudinal muscle runs beneath the dorsal mucosa and acts to shorten the tongue and curl its tip upward. The inferior longitudinal muscle runs along the ventral surface and shortens the tongue while curling the tip downward. The transverse muscle runs horizontally from the median septum to the lateral margins, narrowing and elongating the tongue. The vertical muscle extends from dorsum to ventrum, flattening and broadening the tongue. The extrinsic muscles include the genioglossus, hyoglossus, styloglossus, and palatoglossus. The genioglossus is a fan-shaped muscle arising from the mental spine (genial tubercle) on the inner surface of the mandibular symphysis. Its fibers radiate into the tongue, with the inferior fibers attaching to the hyoid bone. The genioglossus is the primary protruder of the tongue, and bilateral action protrudes the tongue in the midline while unilateral action deviates the tongue to the opposite side. The hyoglossus arises from the hyoid bone and passes vertically into the lateral tongue, acting to depress the tongue. The styloglossus descends from the styloid process to enter the lateral tongue, retracting and elevating the tongue. The palatoglossus arises from the soft palate, descends within the palatoglossal arch, and inserts into the lateral tongue; it elevates the posterior tongue and depresses the soft palate. Motor innervation to all tongue muscles is provided by the hypoglossal nerve (CN XII), with one exception: the palatoglossus is innervated by the vagus nerve via the pharyngeal plexus, reflecting its pharyngeal arch origin. Panel A: Sagittal section showing genioglossus as a large fan from mental spine radiating into tongue and to hyoid bone. Panel B: Hyoglossus as a vertical sheet from hyoid and styloglossus descending from styloid process. Panel C: Intrinsic muscle orientation inset showing longitudinal fibers (superior and inferior), transverse fibers, and vertical fibers. Panel D: Palatoglossus within palatoglossal arch and hypoglossal nerve labeled approaching tongue musculature. --- ## Tongue Innervation The innervation of the tongue is complex, involving multiple cranial nerves for different modalities and different regions. General sensation (touch, pain, temperature) of the anterior two-thirds is carried by the lingual nerve, a branch of the mandibular division of the trigeminal nerve (V3). General sensation of the posterior one-third is provided by the glossopharyngeal nerve (CN IX). The root of the tongue and the epiglottis receive general sensory innervation from the internal laryngeal branch of the vagus nerve (CN X). Taste (special sensation) from the anterior two-thirds is carried by the chorda tympani, a branch of the facial nerve (CN VII). The chorda tympani joins the lingual nerve in the infratemporal fossa, and the taste fibers hitchhike on this nerve to reach the tongue but have their cell bodies in the geniculate ganglion of CN VII. Taste from the posterior one-third is carried by the glossopharyngeal nerve (CN IX). Taste from the small area around the epiglottis is provided by the vagus nerve (CN X). Motor innervation to all intrinsic and extrinsic muscles of the tongue is provided by the hypoglossal nerve (CN XII), except for the palatoglossus, which is innervated by the vagus nerve (CN X) via the pharyngeal plexus. A helpful summary: for the anterior two-thirds, lingual nerve (V3) carries general sensation and chorda tympani (VII) carries taste; for the posterior one-third, glossopharyngeal (IX) carries both general sensation and taste; all muscles are XII except palatoglossus (X). Panel A: Schematic diagram of the tongue divided into anterior two-thirds and posterior one-third by the sulcus terminalis. Panel B: Anterior two-thirds innervation showing lingual nerve (V3, blue) for general sensation and chorda tympani (VII, green) for taste. Panel C: Posterior one-third innervation showing glossopharyngeal nerve (IX, yellow) for both general sensation and taste. Panel D: Motor innervation with hypoglossal nerve (XII, red) to all muscles and asterisk at palatoglossus indicating vagus (X) innervation. --- ## Blood Supply and Lymphatic Drainage of the Tongue The primary arterial supply to the tongue is the lingual artery, a branch of the external carotid artery. The lingual artery passes deep to the hyoglossus muscle (whereas the lingual nerve and hypoglossal nerve pass superficial to it—an important surgical landmark). Within the tongue, the lingual artery divides into the dorsal lingual arteries (supplying the posterior tongue and tonsil region) and the deep lingual artery (the terminal branch, running to the tip of the tongue along with the lingual nerve). Venous drainage is via the lingual veins, which accompany the lingual artery, and the deep lingual veins, which are visible through the mucosa on the undersurface of the tongue and drain into the internal jugular vein. Lymphatic drainage of the tongue is clinically significant because of the tongue's role as a potential site for carcinoma. The tip of the tongue drains to submental nodes. The anterior two-thirds drains laterally to submandibular and upper deep cervical nodes; importantly, the central portion of the anterior tongue may drain bilaterally because lymphatics cross the midline, meaning that midline tumors may metastasize to both sides of the neck. The posterior one-third drains directly to the upper deep cervical nodes, particularly the jugulodigastric node (tonsillar node). The rich lymphatic network of the tongue explains why tongue cancers frequently present with cervical lymph node metastases. Panel A: Lingual artery passing deep to hyoglossus muscle with dorsal and deep lingual branches labeled. Panel B: Lingual veins accompanying the arterial supply with drainage pathways. Panel C: Lymphatic drainage with color-coded arrows showing tip (green) to submental nodes, lateral anterior two-thirds (blue) to submandibular and deep cervical nodes, and posterior one-third (red) directly to deep cervical nodes. Panel D: Note showing bilateral lymphatic drainage potential from midline regions of the tongue. --- ## Salivary Glands Saliva is produced by three pairs of major salivary glands (parotid, submandibular, and sublingual) and numerous minor salivary glands distributed throughout the oral mucosa. The parotid gland is the largest salivary gland and produces purely serous (watery) secretion. It lies in the preauricular region, anterior and inferior to the external ear, and extends from the zygomatic arch superiorly to below the angle of the mandible inferiorly. The facial nerve passes through the gland, dividing it into superficial and deep lobes, but does not supply it. The parotid duct (Stensen's duct) emerges from the anterior border, crosses the masseter muscle, pierces the buccinator, and opens into the vestibule opposite the upper second molar. Parasympathetic secretomotor innervation reaches the gland via a complex pathway: preganglionic fibers from the glossopharyngeal nerve (CN IX) travel via the tympanic and lesser petrosal nerves to synapse in the otic ganglion; postganglionic fibers then hitchhike on the auriculotemporal nerve to reach the gland. The submandibular gland produces mixed secretions, predominantly serous. It lies partly superficial and partly deep to the mylohyoid muscle, wrapping around its posterior border. The submandibular duct (Wharton's duct) is approximately five centimeters long and courses forward through the floor of the mouth to open at the sublingual caruncle, a papilla at the base of the lingual frenulum. The duct is crossed by the lingual nerve, which passes lateral to the duct, then loops under it to emerge medially. Parasympathetic innervation is via the facial nerve (CN VII) through the chorda tympani, which synapses in the submandibular ganglion, with postganglionic fibers reaching the gland directly. The sublingual gland is the smallest of the major glands and produces predominantly mucous secretion. It lies in the floor of the mouth above the mylohyoid muscle, forming a ridge (sublingual fold) in the floor of the mouth. Unlike the other major glands, it has multiple small ducts, some opening separately along the sublingual fold and others joining to form a common duct that may join Wharton's duct or open nearby at the sublingual caruncle. Parasympathetic innervation is the same as for the submandibular gland. Minor salivary glands are scattered throughout the oral mucosa of the lips, cheeks, palate, and tongue, contributing to continuous lubrication of the oral cavity. Panel A: Parotid gland showing location anterior to ear with facial nerve traversing the gland and Stensen's duct crossing masseter to open at upper second molar. Panel B: Submandibular gland wrapping around mylohyoid with Wharton's duct coursing forward to sublingual caruncle and lingual nerve crossing the duct. Panel C: Sublingual gland in floor of mouth with multiple small ducts opening along sublingual fold. Panel D: Summary of secretion type (serous, mixed, mucous) and parasympathetic innervation pathway for each gland. --- ## Floor of the Mouth The floor of the mouth is formed primarily by the mylohyoid muscle, which spans from the mylohyoid line of the mandible to the hyoid bone. Above mylohyoid lie the geniohyoid muscles (paired strap-like muscles from the mental spine to the hyoid) and the genioglossus muscles (attaching to the tongue). The floor of the mouth contains several important structures. The sublingual glands lie above the mylohyoid, covered by mucosa that is elevated as the sublingual folds. The submandibular duct (Wharton's duct) courses through the floor, passing from the deep part of the submandibular gland, between the mylohyoid and hyoglossus muscles, to open at the sublingual caruncle. The lingual nerve enters the floor of the mouth between the medial pterygoid and the mandible, passes lateral to the hyoglossus, then loops under the submandibular duct from lateral to medial (the nerve starts lateral to the duct, passes underneath it, and emerges medial to it). The hypoglossal nerve enters the floor of the mouth beneath the tendon of digastric, runs on the surface of the hyoglossus muscle, and passes forward to supply the tongue musculature. The relationship of the lingual nerve to Wharton's duct is remembered by the mnemonic: "The lingual nerve took a strange course around the Wharton's duct." This relationship is important during surgical procedures on the submandibular gland or during removal of submandibular duct stones. Panel A: Superior view into the floor of mouth with tongue elevated showing mylohyoid muscle as the muscular floor. Panel B: Sublingual gland forming sublingual fold with its multiple duct openings. Panel C: Submandibular duct (Wharton's) coursing forward to sublingual caruncle at base of frenulum with lingual nerve shown crossing lateral to medial beneath the duct. Panel D: Hypoglossal nerve indicated running on hyoglossus toward the tongue musculature. --- ## Palate The palate forms the roof of the oral cavity and the floor of the nasal cavity, separating these two spaces. It consists of the hard palate anteriorly and the soft palate posteriorly. The hard palate is formed by the palatine processes of the maxillae anteriorly and the horizontal plates of the palatine bones posteriorly. Its oral surface is covered by keratinized mucosa and features transverse ridges (rugae) anteriorly that assist in food manipulation. Three foramina penetrate the hard palate. The incisive foramen (anterior, behind the incisors) transmits the nasopalatine nerves and the termination of the greater palatine artery. The greater palatine foramina (posterolateral) transmit the greater palatine nerves and vessels, which supply most of the hard palate. The lesser palatine foramina (posterior to the greater) transmit the lesser palatine nerves and vessels to the soft palate. The soft palate is a mobile musculofascial fold that hangs from the posterior edge of the hard palate. Its free posterior margin bears the uvula centrally and continues laterally as the palatoglossal arch (anterior pillar, containing the palatoglossus muscle) and the palatopharyngeal arch (posterior pillar, containing the palatopharyngeus muscle). The palatine tonsil occupies the triangular tonsillar fossa between these two arches. Five muscles contribute to the soft palate. The tensor veli palatini arises from the base of the skull and the auditory tube cartilage, hooks around the pterygoid hamulus, and spreads into the palate as an aponeurosis; it tenses the soft palate and opens the auditory tube during swallowing. The levator veli palatini arises from the petrous temporal bone and the auditory tube cartilage and inserts into the palatal aponeurosis; it elevates the soft palate to close off the nasopharynx. The palatoglossus descends from the aponeurosis within the palatoglossal arch to insert into the tongue; it elevates the tongue and depresses the palate. The palatopharyngeus descends from the aponeurosis within the palatopharyngeal arch to the pharyngeal wall; it depresses the palate and elevates the pharynx. The musculus uvulae lies within the uvula and shortens it. All soft palate muscles are innervated by the vagus nerve via the pharyngeal plexus, with one exception: the tensor veli palatini is innervated by the mandibular nerve (V3). Panel A: Coronal section showing hard palate formed by maxillary palatine process and palatine bone with incisive and greater palatine foramina. Panel B: Tensor veli palatini hooking around pterygoid hamulus (blue, V3 innervation) and levator veli palatini elevating the palate. Panel C: Palatoglossus and palatopharyngeus forming the anterior and posterior pillars of the fauces. Panel D: Oral view inset showing uvula, palatoglossal and palatopharyngeal arches, and tonsillar fossa. --- ## Pharynx Overview The pharynx is a muscular tube extending from the skull base to the level of the C6 vertebra, where it becomes continuous with the esophagus. It serves as a common pathway for air (from the nose to the larynx) and food (from the mouth to the esophagus). Its length is approximately twelve to fourteen centimeters. The pharynx is divided into three regions based on the structures that open into it. The nasopharynx lies behind the nasal cavity, extending from the skull base to the level of the soft palate. It is purely respiratory in function. The oropharynx lies behind the oral cavity, extending from the soft palate to the upper border of the epiglottis (approximately the level of C3). It transmits both air and food. The laryngopharynx (hypopharynx) lies behind the larynx, extending from the upper border of the epiglottis to the lower border of the cricoid cartilage at C6, where it becomes continuous with the esophagus. It transmits food around the laryngeal inlet and into the esophagus. The nasopharynx contains the pharyngeal tonsil (adenoids) on its posterior wall, the openings of the auditory (Eustachian) tubes on its lateral walls, and the tubal tonsils surrounding these openings. The oropharynx contains the palatine tonsils between the palatoglossal and palatopharyngeal arches, and the posterior third of the tongue (with its lingual tonsil) forms its anterior wall. The laryngopharynx contains the piriform fossae, recesses on either side of the laryngeal inlet where food is directed around the larynx, and it is bounded anteriorly by the posterior surface of the larynx. Panel A: Midsagittal section showing nasopharynx (blue) from skull base to soft palate with adenoids on posterior wall and auditory tube opening. Panel B: Oropharynx (green) from soft palate to epiglottis with palatine and lingual tonsils. Panel C: Laryngopharynx (yellow) from epiglottis to C6 with piriform fossae lateral to laryngeal inlet. Panel D: Vertebral levels C1-C6 indicated alongside the three pharyngeal divisions. --- ## Pharyngeal Walls and Muscles The pharyngeal wall consists of four layers from inside out: mucosa, pharyngobasilar fascia (a fibrous submucosa that attaches the pharynx to the skull base), the muscular layer, and the buccopharyngeal fascia externally. The muscular layer comprises three circular constrictor muscles and three longitudinal muscles. The constrictor muscles overlap like stacked cups, with each upper muscle's lower fibers lying inside the next muscle's upper fibers. The superior constrictor arises from the pterygoid hamulus, the pterygomandibular raphe, the mylohyoid line of the mandible, and the tongue. It attaches posteriorly to the pharyngeal tubercle on the occipital bone and the pharyngeal raphe in the midline. The middle constrictor arises from the hyoid bone and the stylohyoid ligament and fans out to attach to the pharyngeal raphe. The inferior constrictor arises from the oblique line of the thyroid cartilage and the arch of the cricoid cartilage; its lower fibers from the cricoid (cricopharyngeus) function as the upper esophageal sphincter. The gaps between the constrictors are clinically important because they transmit structures and may be sites of weakness. Above the superior constrictor (between it and the skull base), the levator veli palatini and the auditory tube enter the nasopharynx. Between the superior and middle constrictors, the stylopharyngeus muscle and the glossopharyngeal nerve (CN IX) enter the pharynx. Between the middle and inferior constrictors, the internal laryngeal nerve and superior laryngeal vessels pierce the thyrohyoid membrane to enter the pharynx. Below the inferior constrictor, above the cricopharyngeus, lies Killian's dehiscence, a potential weak point where pharyngeal mucosa may herniate to form a Zenker's diverticulum. The longitudinal muscles include the stylopharyngeus (from the styloid process, passing between the superior and middle constrictors to blend with the pharyngeal wall), the palatopharyngeus (from the palate, descending within the palatopharyngeal arch to the thyroid cartilage and pharyngeal wall), and the salpingopharyngeus (from the auditory tube, descending to blend with the palatopharyngeus). The stylopharyngeus is innervated by the glossopharyngeal nerve (CN IX), and it is the only muscle that nerve supplies motorically. The other two longitudinal muscles are innervated by the vagus via the pharyngeal plexus. Panel A: Posterior view of the pharynx with posterior wall opened showing overlapping constrictor muscles (superior, middle, inferior) like nested cups with their origins indicated. Panel B: Gaps between constrictors labeled -- auditory tube and levator above superior constrictor, stylopharyngeus and CN IX between superior and middle. Panel C: Internal laryngeal nerve between middle and inferior constrictors, and Killian's dehiscence below inferior constrictor. Panel D: Longitudinal muscles (stylopharyngeus, palatopharyngeus) shown on the internal surface of the pharyngeal wall. --- ## Waldeyer's Ring Waldeyer's tonsillar ring is a ring of lymphoid tissue encircling the entrances to the respiratory and digestive tracts at the junction of the oral and nasal cavities with the pharynx. This tissue represents the first line of immunological defense against inhaled and ingested pathogens. The components of Waldeyer's ring include the pharyngeal tonsil (adenoids), located on the posterior wall and roof of the nasopharynx; the tubal tonsils, surrounding the openings of the auditory tubes in the lateral nasopharynx; the palatine tonsils (commonly referred to simply as "the tonsils"), located between the palatoglossal and palatopharyngeal arches in the oropharynx; and the lingual tonsil, consisting of lymphoid nodules on the posterior third of the tongue. The palatine tonsils deserve particular attention due to their clinical significance. Each tonsil sits in the triangular tonsillar fossa between the anterior pillar (palatoglossal arch) and the posterior pillar (palatopharyngeal arch). The tonsil is covered medially by stratified squamous epithelium with deep crypts that trap pathogens. Laterally, a fibrous capsule separates the tonsil from the superior constrictor muscle. The blood supply is primarily from the tonsillar branch of the facial artery, with contributions from the ascending palatine, ascending pharyngeal, and dorsal lingual arteries. A peritonsillar venous plexus drains to the pharyngeal plexus. Sensory innervation is from the glossopharyngeal nerve (CN IX), which explains the referred pain to the ear (via the tympanic branch of IX) that accompanies tonsillitis. Panel A: Waldeyer's ring shown schematically as a circular arrangement of lymphoid tissue with pharyngeal tonsil (adenoids) superoposteriorly in the nasopharynx. Panel B: Tubal tonsils bilaterally around auditory tube openings and palatine tonsils laterally between pillars in the oropharynx. Panel C: Lingual tonsil inferiorly on tongue base completing the ring. Panel D: Inset showing close-up of palatine tonsil in tonsillar fossa between arches with blood supply from tonsillar branch of facial artery. --- ## Clinical Correlations Tonsillitis is inflammation of the palatine tonsils, commonly caused by viral or bacterial (especially Group A Streptococcus) infection. It presents with sore throat, dysphagia, fever, and cervical lymphadenopathy. Untreated streptococcal tonsillitis may lead to complications including peritonsillar abscess (quinsy), rheumatic fever, or post-streptococcal glomerulonephritis. A peritonsillar abscess (quinsy) is a collection of pus between the tonsillar capsule and the superior constrictor muscle, presenting with severe throat pain, "hot potato" voice, trismus, and uvular deviation away from the affected side. It may spread to the parapharyngeal space and requires drainage. Adenoid hypertrophy is enlargement of the pharyngeal tonsil, most commonly in children. Symptoms include nasal obstruction, mouth breathing, hyponasal speech, and snoring. Chronic enlargement may obstruct the auditory tube, leading to recurrent otitis media and conductive hearing loss. The characteristic "adenoid facies" includes open mouth, elongated face, and dental malocclusion. Hypoglossal nerve palsy causes paralysis of the ipsilateral tongue muscles. At rest, the tongue may show atrophy and fasciculations on the affected side. When protruded, the tongue deviates toward the paralyzed side because the intact genioglossus on the opposite side pushes the tongue across the midline while the paralyzed genioglossus cannot. Causes include brainstem lesions, skull base tumors, and neck surgery. Submandibular duct stones (sialolithiasis) are most common in Wharton's duct, accounting for approximately eighty percent of salivary stones. This predilection is explained by the duct's length, its upward course against gravity, and the relatively viscous secretion of the submandibular gland. Patients present with painful swelling of the submandibular gland that worsens with meals (salivary colic). Ludwig's angina is a rapidly spreading cellulitis of the submandibular space, typically originating from dental infections of the lower molars. It can spread to involve the floor of the mouth and may compromise the airway by elevating and displacing the tongue posteriorly. This is a surgical emergency requiring aggressive airway management and drainage. Zenker's diverticulum is a false (mucosal) diverticulum that herniates through Killian's dehiscence, the area of weakness between the oblique (thyropharyngeus) and horizontal (cricopharyngeus) fibers of the inferior constrictor. It typically occurs in elderly patients and presents with dysphagia, regurgitation of undigested food, halitosis, and aspiration risk. Panel A: Peritonsillar abscess showing unilateral tonsillar swelling with uvular deviation. Panel B: Tongue protrusion in hypoglossal nerve palsy showing deviation toward the lesion side with ipsilateral atrophy. Panel C: Submandibular gland with stone visible in Wharton's duct on floor of mouth radiograph. Panel D: Barium swallow showing Zenker's diverticulum as a posterior pharyngeal pouch. --- ## Summary The oral cavity is divided into the vestibule (between lips/cheeks and teeth) and the oral cavity proper (within the dental arches). The tongue has intrinsic muscles (changing shape) and extrinsic muscles (moving the tongue), all innervated by the hypoglossal nerve (CN XII) except the palatoglossus (CN X). Sensory innervation of the anterior two-thirds is via the lingual nerve (V3) for general sensation and chorda tympani (VII) for taste; the posterior one-third receives both modalities from the glossopharyngeal nerve (IX). The three major salivary glands are the parotid (serous, opening at upper second molar), submandibular (mixed, opening at sublingual caruncle), and sublingual (mucous, multiple small openings). The pharynx comprises three parts: nasopharynx (behind nasal cavity), oropharynx (behind oral cavity), and laryngopharynx (behind larynx). The three constrictor muscles overlap from above, with gaps transmitting important structures. Waldeyer's ring consists of the pharyngeal, tubal, palatine, and lingual tonsils forming a defensive ring at the pharyngeal entrance. --- ## Key Terms | Term | Definition | |------|------------| | Sulcus terminalis | V-shaped groove on the tongue dorsum dividing the anterior two-thirds from the posterior one-third | | Wharton's duct | Submandibular gland duct opening at the sublingual caruncle at the base of the frenulum | | Palatoglossal arch | Anterior pillar of the fauces containing the palatoglossus muscle | | Waldeyer's ring | Ring of lymphoid tissue (pharyngeal, tubal, palatine, and lingual tonsils) at the pharyngeal entrance | | Killian's dehiscence | Weak area between thyropharyngeus and cricopharyngeus muscles; site of Zenker's diverticulum | | Piriform fossa | Recess on either side of the laryngeal inlet in the laryngopharynx | --- *This content is subject to the [MIT License](https://opensource.org/licenses/MIT). © 2024–2026 Hibbert School of Medicine.*