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Consists of 2 parts: oral vestibule and oral cavity proper 

Oral vestibule is bounded by the lips and cheeks externally and the teeth and gums internally 

• Receives the opening of the parotid duct at the parotid papilla opposite the second maxillary molar

Oral cavity proper is bounded anteriorly and laterally by the teeth and gums. Its roof is formed by the hard palate. Its floor is formed by the tongue and mucosa, supported by geniohyoid and mylohyoid muscles. It communicates posteriorly with oropharynx. 

Teeth

Teeth are anchored individually into alveoli (sockets) in the alveolar processes of the maxillae and mandible by periodontal ligaments.

In each quadrant of the jaws, there are 2 incisors for cutting, 1 canine for tearing, 2 premolars and 3 molars used for grinding

Maxillary teeth are innervated by V2 branches (anterior,middle, posterior superior alveolar nerves) 

Mandibular teeth are innervated by V3 (inferior alveolar nerves).

Palate

 The palate forms the roof of the mouth and the floor of the nasal cavities, thereby separating the nasal cavity from the oral cavity. Its superior surface is covered by respiratory mucosa, while its inferior surface is covered by oral mucosa.

The hard palate is formed by palatal processes of the maxillae and horizontal plates of the palatine bones. The posterior border of the hard palate has a palatine aponeurosis for attachment of soft palate musculature. The hard palate is considered part of the oral cavity proper, while the soft palate is part of the oropharynx. 

The soft palate contains no bony framework; instead, it contains a membranous aponeurosis. It hangs from the posterior aspect of the hard palate and separates the nasopharynx from the oropharynx. Its posterior extension is termed the uvula.

The soft palate functions to: 

• Close oropharyngeal isthmus by bringing the dorsum of tongue and soft palate together, sealing the oral cavity from the oropharynx. 
  • Oropharyngeal isthmus (Fauces) = the narrow passage from the mouth to the pharynx situated between the soft palate and the base of the tongue
• Separate the oropharynx from nasopharynx by elevating the soft palate and pushing it against posterior wall of pharynx. This occurs during swallowing, preventing food from passing into nasopharynx and nasal cavity.

The  pillars of the fauces bound the oropharyngeal isthmus laterally. 

• The anterior pillar is the palatoglossal arch/fold, which consists of the palatoglossus muscle covered by mucosa.
• The posterior pillar is the palatopharyngeal arch/fold, which consists of the palatopharyngeus muscle covered by mucosa.

The palatine tonsils are covered by mucosa and are located in the tonsillar sinus between the palatoglossal and palatopharyngeal arches. The palatine tonsils receive a rich vascular supply from facial, ascending pharyngeal, lesser palatine and dorsal lingual arteries.

The palatine tonsils form part of Waldeyer’s ring of lymphoid tissue, which guards the oropharyngeal entrance. Other components of Waldeyer’s ring are: pharyngeal tonsils (adenoids), lingual tonsils and tubal tonsils (on auditory tube).

Muscles of the soft palate:

⚠️ CN X innervates all muscles of the palate except tensor veli palatini CN V3.

• Palatoglossus originates from the palatine aponeurosis and inserts into the side of the tongue. It is covered by mucous membrane, forming palatoglossal arch (anterior pillar of fauces). It depresses the soft palate to seal the oropharyngeal isthmus; closes the oral cavity from the oropharynx.
• Palatopharyngeus originates from palatine aponeurosis and inserts into lateral wall of pharynx. Together with its overlying mucosa, it forms the palatopharyngeal arch. It depresses soft palate to seal the oropharyngeal isthmus; closes the oral cavity from the oropharynx.
• Levator veli palatini originates from the medial aspect of the auditory tube and inserts into the palatine aponeurosis. It elevates soft palate to seal the nasopharynx from the oropharynx and opens the pharyngeal orifice of the auditory tube.
  
• Tensor veli palatini originates from the lateral aspect of the auditory tube & scaphoid fossa of the sphenoid. Its fibers pass along the medial aspect of the medial pterygoid plate. Its tendon hooks over the hamulus and then spreads to blend with the palatine aponeurosis. This muscle uses the hamulus as a pulley in order to tense the soft palate. It also acts to open the pharyngeal orifice of the auditory tube.
  
• Musculus uvulae originates from the posterior nasal spine and inserts into the uvula. It shortens the uvula and pulls it superiorly to seal the nasopharynx.
  

Tongue

The tongue consists of two general parts: a mobile body - anterior ⅔ - found in the oral cavity and a base - posterior ⅓ - that passes into the oropharynx and is fixed to the hyoid bone.

The dorsum of the tongue exhibits two sulci:  

• Median sulcus: shallow midline groove separating the tongue into left and right halves 
• Sulcus terminalis: a V shaped groove separating the anterior 2/3 from the posterior 1/3.

The foramen cecum is a small pit-like depression located at the apex of sulcus terminalis. This depression represents the embryological site through which the thyroid gland descended into the neck.

The anterior ⅔ of the tongue is covered by papillae on its dorsal surface. 

• Filiform papillae are the most numerous. They give the dorsum a rough texture. 
• Fungiform papillae are interspersed among the filiform papillae and are located mainly at tip and lateral margins. They bear taste buds. 
• Circumvallate (vallate) papillae lie just anterior to the sulcus terminalis and are supplied with taste buds. 
• Foliate papillae are located at the lateral margins of tongue and are rudimentary in humans.

The posterior ⅓ of the tongue is covered by lingual tonsils, which appear as irregular bulges in the mucosa. They contribute to the tonsillar ring of lymphoid tissue encircling the oropharyngeal opening called Waldeyer’s ring.

Glossoepiglottic folds are mucosal folds that run anteriorly from the epiglottis to the base of the posterior ⅓ of the tongue. There is a median and two lateral glossoepiglottic folds.

The ventral (sublingual) surface of the tongue is smooth. The lingual frenulum is a thin fold of mucosa that attaches the anterior ⅔ to the floor of the mouth. By following the frenulum to the floor of the mouth, the sublingual caruncula or papillae can be identified as enlarged papillae adjacent to the frenulum. The orifices of the submandibular ducts (Wharton’s ducts) are located on these sublingual papillae. The plica sublingualis (sublingual fold) is a mucosal elevation overlying sublingual glands on the floor of the mouth. The deep lingual veins are located on either side of the frenulum and are covered by mucosal folds called plicae fimbriatae.

Muscles of the tongue 

Intrinsic musculature is contained within the tongue and acts to alter the tongue’s shape. Three type of fibers constitute the intrinsic musculature: longitudinal, transverse and vertical.

Extrinsic muscles of the tongue originate from the mandible, hyoid bone or styloid process and insert into the tongue. 

• Hyoglossus originates from the hyoid bone and inserts into the lateral aspect of the tongue. It depresses the dorsum of the tongue and aids in retraction of the tongue
• Styloglossus originates from the styloid process and inserts into the lateral aspect of the tongue. It draws up the sides of the tongue to create a trough for swallowing and aids in retracting the tongue.
• Genioglossus originates from the superior mental spine (genial tubercle) of the mandible. Its superior fibers attach to the tip of tongue; its middle fibers insert into the dorsum of tongue; its inferior fibers attach to the hyoid bone. This muscle pulls the dorsum anteriorly to protrude the tongue, while its superior fibers retract tip of tongue and pull it inferiorly
  
• Palatoglossus is a muscle of the soft palate that attaches to the tongue. It acts to close the oropharyngeal isthmus by approximating the tongue and soft palate. 
  

⚠️ CN XII (hypoglossal nerve) provides motor innervation to all intrinsic and extrinsic muscles of tongue EXCEPT palatoglossus (CN X).

Floor of Mouth (FOM) 

The floor of mouth is located between the medial aspect of the body of the mandible above the mylohyoid line and the base of the tongue. Inferiorly, the mylohyoid limits the floor of the mouth. A number of structures are located in the floor of the mouth, including the lingual nerve and submandibular ganglion, lingual artery, glossopharyngeal and hypoglossal nerves, as well as sublingual and submandibular salivary glands.

Lingual artery arises as a branch of the external carotid artery and passes between the genioglossus and the hyoglossus into the floor of the mouth. It gives rise to three sets of branches: 

• Dorsal lingual branches: posterior one third of tongue 
• Sublingual branch: sublingual glands and floor of mouth 
• Deep lingual artery: provides blood to the anterior ⅔ of tongue

Submandibular gland is located in the submandibular triangle and in the floor of mouth. It wraps around the posterior border of the mylohyoid and passes into the floor of the mouth. This deep portion extends anteriorly between the body of mandible and base of tongue as far as the second molar. Here it forms the submandibular duct (Wharton’s duct), which travels between the sublingual gland and the body of the tongue. The duct passes anteriorly between mylohyoid, hyoglossus and genioglossus ending anteriorly by opening onto the sublingual papilla just lateral to midline lingual frenulum.

Sublingual gland is located entirely in the floor of the mouth. It is bounded laterally by the sublingual fossa of the mandible and medially by the base of the tongue. It has 12 ducts (of Rivinus) which drain upward through the sublingual fold into the oral cavity.

Innervation

Preganglionic parasympathetic fibers originate in the superior salivatory nucleus. They exit the brainstem via CN VII and enter the internal acoustic meatus. In the temporal bone, chorda tympani branches from CN VII; it emerges into the infratemporal fossa via the petrotympanic fissure.

Chorda tympani joins the lingual nerve in the infratemporal fossa. Its preganglionic parasympathetic fibers pass into the submandibular ganglion where they synapse. Postganglionic parasympathetic fibers innervate the submandibular gland directly or rejoin the lingual nerve to reach the sublingual gland. Postganglionic sympathetic fibers from the superior cervical ganglion follow the lingual artery and also innervate the salivary glands. Parasympathetic fibers regulate water and electrolyte release, while sympathetic fibers induce protein secretion (thicker saliva).

Parotid gland is closely related to the ramus of the mandible. The parotid duct (of Stenson) crosses the masseter, pierces the buccinator and empties into the oral cavity opposite the 2nd maxillary molar on either side.