Oral Cavity, Tongue and Salivary Glands

Oral vestibule:

• The slit-like space between the lips/cheeks (externally) and the teeth/gums (internally), receives the opening of the parotid duct (opposite the second upper molar) and numerous minor salivary gland ducts.

Oral cavity proper:

• The space internal to the teeth/gums, bounded by the hard/soft palate (roof), the tongue and floor of mouth (floor), and continuous posteriorly with the oropharynx at the oropharyngeal isthmus (marked by the palatoglossal folds/arches).

Lips:

• Formed predominantly by orbicularis oris, covered externally by skin and internally by mucosa, with the characteristic vermilion border marking the transition zone.

Cheeks:

• Formed predominantly by buccinator, forming the lateral walls of the oral cavity/vestibule.

Floor of mouth:

• Formed by the mylohyoid muscle (a muscular sling), supporting the tongue and the sublingual/submandibular gland structures, with the midline lingual frenulum connecting the tongue's undersurface to the floor.

Hard palate:

• The anterior, bony two-thirds, formed by the palatine processes of the maxilla and the horizontal plates of the palatine bones, separates the oral and nasal cavities.

Soft palate:

• The posterior, mobile, muscular one-third, extending from the hard palate's posterior border to the free-hanging uvula, forming a mobile partition that elevates during swallowing/phonation to close off the nasopharynx (preventing nasal regurgitation of food/fluid and nasal air escape during certain speech sounds).

Palatal muscles:

• Innervation summary: All palatal muscles are vagus nerve (CN X)-innervated except tensor veli palatini, which is trigeminal (CN V3)-innervated. This is a frequently tested exception.
• It parallels the analogous single exceptions seen with palatoglossus among tongue muscles and tensor tympani among the ear ossicular muscles (Section 8).
• All three exceptions share a first-arch (trigeminal) developmental origin against an otherwise different surrounding pattern.

Apex: The mobile, anterior tip.

Body: The anterior two-thirds, freely mobile, lying within the oral cavity proper.

Root: The posterior one-third, relatively fixed, lying within the oropharynx.

Dorsal surface: Divided into anterior (oral, papillated) and posterior (pharyngeal, lymphoid, containing the lingual tonsil) parts by the terminal sulcus, a V-shaped groove.

Terminal sulcus: The dividing line between the tongue's anterior two-thirds (oral part, developmentally derived from the first pharyngeal arch) and posterior one-third (pharyngeal part, from the third/fourth arches). This embryological division underlies the differing innervation pattern of the two regions.

Foramen caecum: A small midline pit at the apex of the terminal sulcus, marking the embryological origin site of the thyroid gland (the point from which the thyroid diverticulum descended during development).

It is the potential site of a thyroglossal duct cyst if the normal thyroglossal duct fails to fully involute (see Applied Anatomy).

Filiform papillae:

• The most numerous, covering most of the anterior dorsal tongue, providing a rough/mechanical texture (aiding food manipulation) but containing no taste buds.

Fungiform papillae:

• Mushroom-shaped, scattered among the filiform papillae (more concentrated at the tip/margins), each containing a variable number of taste buds.

Circumvallate papillae:

• Large, distinctive papillae arranged in a V-shaped row immediately anterior to the terminal sulcus (typically 8-12 papillae), each surrounded by a circular trench and containing numerous taste buds.
• Also associated with von Ebner's glands: serous glands secreting into the surrounding trench, helping to "reset" the taste receptors between different tastants.

Foliate papillae:

• Vertical, leaf-like folds on the posterolateral tongue margins, containing taste buds, relatively rudimentary/vestigial in humans compared to some other mammals.

Intrinsic Muscles

• Alter the shape of the tongue (without changing its overall position), all innervated by the hypoglossal nerve (CN XII).

Extrinsic Muscles

• Alter the position of the tongue, all innervated by the hypoglossal nerve (CN XII) except palatoglossus (vagus nerve, via pharyngeal plexus).

Motor:

• All tongue muscles (intrinsic and extrinsic): hypoglossal nerve (CN XII), except palatoglossus (vagus nerve, CN X, via pharyngeal plexus).

General sensation:

• Anterior two-thirds: Lingual nerve (branch of the mandibular division, CN V3).
• Posterior one-third: Glossopharyngeal nerve (CN IX).
• Extreme posterior (valleculae/epiglottic region): Internal laryngeal nerve (branch of the vagus, CN X, via the superior laryngeal nerve).

Taste:

• Anterior two-thirds: Facial nerve (CN VII), via the chorda tympani, which joins the lingual nerve peripherally to reach the tongue.
• The taste fibres' ultimate central connection is the facial nerve, not trigeminal. This is a classic "different nerve for general sensation vs taste in the same territory" pattern. Contrast it directly against the posterior third, where the same nerve, CN IX, carries both modalities.
• Posterior one-third: Glossopharyngeal nerve (CN IX), carries both general sensation AND taste here, unlike the anterior two-thirds' split arrangement.
• Extreme posterior (valleculae/epiglottic region): Vagus nerve (CN X), via the internal laryngeal nerve, carries both general sensation and taste here too.

• Organising summary table:

Lingual artery:

• A branch of the external carotid artery, passing deep to hyoglossus (a key surgical landmark), giving rise to the dorsal lingual, sublingual, and deep lingual arteries, supplying the entire tongue.

• Tongue lymphatic drainage follows a pattern based on tongue region, with important bilateral crossover drainage from the midline structures: a clinically critical feature for cancer staging/spread patterns.

• Tip: Drains to the submental nodes (bilaterally, given the tip's midline position).
• Lateral anterior tongue: Drains to the submandibular nodes (predominantly ipsilateral).
• Central anterior tongue: Drains bilaterally (given its midline position) to both submandibular and deep cervical nodes.
• This bilateral drainage from midline tongue structures is the key reason why tongue cancers arising near the midline carry a higher risk of bilateral cervical lymph node metastasis. It complicates surgical/oncological management compared to more laterally-positioned lesions.
• Posterior tongue: Drains directly and bilaterally to the deep cervical nodes (particularly the jugulodigastric node), bypassing the submandibular/submental groups entirely.

Parotid Gland

• Position: The largest salivary gland, located anterior to and below the external ear, overlying the ramus of the mandible and masseter muscle, extending into the space between the mandible ramus and the mastoid process/sternocleidomastoid.
• Relations: The facial nerve runs through the gland's substance. For descriptive surgical purposes it divides the gland into superficial and deep lobes, though this is not a true anatomical fascial division.
• The gland also contains the retromandibular vein and the external carotid artery, both passing through the gland's substance, deep to the facial nerve plane.
• This "nerve most superficial, vein intermediate, artery deepest" layering within the gland is a critical surgical anatomy concept for parotidectomy.
• Duct (parotid/Stensen's duct): Emerges from the anterior gland border, crosses masseter superficially, pierces buccinator, opens into the oral vestibule opposite the second upper molar tooth.
• Blood supply: Branches of the external carotid artery (as it passes through the gland) and the superficial temporal artery.
• Parasympathetic innervation: From the otic ganglion. Preganglionic fibres travel via the glossopharyngeal nerve → tympanic nerve → lesser petrosal nerve → otic ganglion, synapsing there.
• Postganglionic fibres then travel via the auriculotemporal nerve, a branch of CN V3, to reach the gland. This is a notable pathway where the postganglionic fibres "hitchhike" on a different cranial nerve's branch than the one that carried the preganglionic fibres.
• Lymphatics: Drain to the parotid (preauricular) lymph nodes, both superficial (within the capsule) and deep (within the gland substance) groups.

Submandibular Gland

• Position: Located partly superficial to and partly deep to the mylohyoid muscle (which forms the floor of the submandibular triangle), the gland effectively wraps around the mylohyoid's posterior free border.
• Relations: Closely related to the lingual nerve (which loops beneath the submandibular duct in a characteristic "hooking" relationship, of major surgical significance) and the hypoglossal nerve (running deep to the gland).
• Duct (submandibular/Wharton's duct): Arises from the deep part of the gland, runs forward along the floor of the mouth, opens at the sublingual caruncle, a small papilla on either side of the lingual frenulum.
• Its relatively long course makes this duct particularly prone to calculus (stone) formation (see Applied Anatomy). Saliva must flow "uphill" against gravity from the gland to this anterior opening.
• Blood supply: Facial artery (which grooves the gland's posterior/superior surface before crossing the mandible) and lingual artery.
• Parasympathetic innervation: From the submandibular ganglion (preganglionic fibres via the facial nerve → chorda tympani → lingual nerve → submandibular ganglion, synapsing there; postganglionic fibres then directly supply the gland, along with the nearby sublingual gland).
• Lymphatics: Drain to the submandibular lymph nodes.

Sublingual Gland

• Position: The smallest of the three major salivary glands, located in the floor of the mouth, superior to mylohyoid, anterior to the submandibular gland's deep part.
• Relations: Closely related to the lingual nerve and the submandibular duct, both of which pass along its medial/superior surface.
• Duct: Unlike the other two major glands, has multiple small ducts (typically 8-20, termed the ducts of Rivinus) opening directly along the floor of the mouth, though a larger duct (of Bartholin) sometimes joins the submandibular duct.
• Blood supply: Sublingual artery (branch of the lingual artery) and submental artery (branch of the facial artery).
• Parasympathetic innervation: Same pathway as the submandibular gland, from the submandibular ganglion, via postganglionic fibres that reach the sublingual gland directly (a shared parasympathetic supply pathway for both glands, despite them being anatomically distinct structures).
• Lymphatics: Drain to the submandibular lymph nodes (alongside the submandibular gland's own drainage).

Tongue deviation:

• Unilateral hypoglossal nerve (CN XII) lesion causes the protruded tongue to deviate toward the affected (weak) side, given unopposed contralateral genioglossus action.

Lingual nerve injury:

• The lingual nerve has a close, "hooking" relationship to the submandibular duct, passing lateral to, then beneath, then medial to the duct as it courses toward the tongue. This makes it vulnerable to iatrogenic injury during submandibular gland excision or submandibular duct stone removal.
• Injury causes loss of general sensation over the anterior two-thirds of the tongue. Given the chorda tympani's peripheral course alongside it, taste is also lost over the same region.

Salivary duct stones (sialolithiasis):

• Most commonly affect the submandibular duct. Its relatively long, uphill (against gravity) course and its more viscous, mucous-rich (rather than purely serous) saliva both predispose to stasis and subsequent calculus formation.
• Presents with painful, meal-related swelling of the gland, as saliva production increases with eating but cannot adequately drain past the obstructing stone.

Parotid surgery:

• The critical anatomical consideration is the facial nerve's course through the gland's substance. Parotidectomy requires careful identification and preservation of the nerve's branches.
• The branches are typically identified at the main trunk as it exits the stylomastoid foramen, then traced forward through the gland. Iatrogenic facial nerve injury during this surgery has serious functional and cosmetic consequences.