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Anatomy of the Tongue

Overview

• Anterior two-thirds (oral tongue) - mobile portion in the oral cavity
• Posterior one-third (tongue base / base of tongue) - fixed portion in the oropharynx

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Surface Anatomy

Papillae (anterior two-thirds)

Other Surface Features

• Frenulum - anterior fold of mucous membrane tethering the inferior tongue to the floor of the mouth; Wharton's ducts (submandibular gland) open on either side; may be congenitally short (ankyloglossia / "tongue-tie")
• Lingual tonsil - lymphoid tissue at the base of tongue (oropharynx)
• Valleculae - depressions on either side of the midline glossoepiglottic fold, extending to the pharyngoepiglottic fold laterally

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Muscles

Extrinsic Muscles (move the tongue as a whole)

Key point: Palatoglossus is the only tongue muscle NOT innervated by CN XII - it is innervated by the vagus nerve via the pharyngeal plexus.

Intrinsic Muscles (change shape of the tongue)

Fibrous Septum (Septum Linguae)

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Vascular Supply

• Arterial: Lingual artery - the 2nd branch of the external carotid artery (some sources cite it as the 3rd)
  • Branches: dorsal lingual, sublingual, and deep lingual arteries
• Venous drainage: Lingual vein and vena comitans of the hypoglossal nerve (Ranine vein)

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Lymphatic Drainage

The bilateral drainage of the posterior tongue is clinically significant - cancers of the tongue base can metastasize to the contralateral neck.

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Sensory Innervation

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Taste (Special Sensory)

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Motor Innervation Summary (CN XII - Hypoglossal)

• All intrinsic muscles
• Genioglossus, hyoglossus, styloglossus
• Genioglossus is the most important clinically - loss of its tone (e.g., in unconsciousness or CN XII palsy) causes the tongue to fall backwards and obstruct the airway
• In CN XII palsy, the tongue deviates toward the side of the lesion on protrusion (unopposed genioglossus on the intact side pushes the tongue to the affected side)

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Tongue - High-Yield Viva Points

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1. Parts & Basic Description

• Muscular organ of deglutition, taste, and speech
• Partly oral, partly pharyngeal in position
• Divided into anterior 2/3 (oral tongue) and posterior 1/3 (tongue base/root)
• Separated by the sulcus terminalis - a V-shaped groove
• At the apex of the sulcus terminalis lies the foramen cecum - the embryologic origin of thyroid descent

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2. Papillae (Classic Viva Question)

Viva point: Filiform papillae are the ONLY papillae with NO taste buds. They have a mechanical/masticatory function - increase friction between tongue and food.

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3. Muscles

Rule to remember:

All tongue muscles = CN XII, EXCEPT palatoglossus = CN X (vagus)

Extrinsic Muscles

Intrinsic Muscles (all CN XII)

Viva point: Genioglossus is the most clinically important tongue muscle - loss of tone (e.g., unconsciousness, CN XII palsy) causes tongue to fall back and obstruct the airway.

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4. Nerve Supply (Most Asked!)

Motor

• CN XII (Hypoglossal) - all intrinsic + extrinsic muscles except palatoglossus
• CN X (Vagus) - palatoglossus only

Sensory (General)

• Anterior 2/3 - Lingual nerve (CN V3)
• Posterior 1/3 - Glossopharyngeal nerve (CN IX)

Taste (Special Sensory)

• Anterior 2/3 - Chorda tympani (branch of CN VII) via lingual nerve
• Posterior 1/3 - CN IX
• Extreme posterior + epiglottis - Superior laryngeal nerve (CN X)

Viva trick: Sensory and taste are supplied by DIFFERENT nerves on the anterior 2/3 - touch by CN V3, taste by CN VII (chorda tympani).

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5. Blood Supply

• Arterial: Lingual artery (branch of external carotid artery)
• Venous: Lingual vein + Ranine vein (vena comitans of hypoglossal nerve)

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6. Lymphatic Drainage

Viva point: Posterior tongue drains bilaterally - this is WHY carcinoma of tongue base can metastasize to the contralateral neck, requiring bilateral neck dissection.

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7. Embryology

• Tongue appears at 4 weeks
• Anterior 2/3 - from 2 lateral lingual swellings + 1 tuberculum impar (all from 1st pharyngeal arch) → sensory by CN V3
• Posterior 1/3 - from copula (2nd, 3rd, 4th arch); 3rd arch tissue overgrows 2nd → sensory by CN IX
• Tongue muscles - derived from occipital somite myoblasts migrating into the tongue → hence innervated by CN XII (hypoglossal)
• Foramen cecum = site where thyroid diverticulum invaginates → thyroid descends from here; persistence gives thyroglossal duct cyst or lingual thyroid

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8. Clinical Viva Points

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9. One-Liner Facts Examiners Love

• Undersurface of tongue - no papillae; has frenulum, lingual vein, and fimbriated fold
• Lingual tonsil - lymphoid tissue on posterior 1/3 (pharyngeal surface); no papillae on this surface
• Valleculae - depressions on either side of the midline glossoepiglottic fold; part of oropharynx
• Fibrous septum (septum linguae) - divides tongue into two halves; contains a triangular fat pad visible on axial CT
• Wharton's duct (submandibular gland) opens on either side of the frenulum
• Only 8-12 circumvallate papillae despite being the largest and most prominent

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• Gray's Anatomy for Students
• Color Atlas of Human Anatomy (Vols 1, 2, 3)
• Netter's Atlas of Human Anatomy
• THIEME Atlas of General Anatomy
• Color Atlas of Ultrasound Anatomy

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Tongue - Viva Points

Source: Gray's Anatomy for Students

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Fig. 8.257 - Tongue Overview (Gray's)

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1. Definition & Basic Description

• The tongue is a muscular structure forming part of the floor of the oral cavity and part of the anterior wall of the oropharynx
• Anterior part is in the oral cavity - somewhat triangular in shape with a blunt apex directed anteriorly, sitting immediately behind the incisor teeth
• The root of the tongue is attached to the mandible and the hyoid bone

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2. Parts of the Tongue

• Separated by a V-shaped terminal sulcus
• The terminal sulcus forms the inferior margin of the oropharyngeal isthmus between oral and pharyngeal cavities
• At the apex of the V = foramen cecum - the site where epithelium invaginated in the embryo to form the thyroid gland
• In some individuals a thyroglossal duct persists, connecting the foramen cecum to the thyroid gland in the neck

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3. Surfaces

Dorsal (Superior) Surface

• Anterior 2/3 covered by hundreds of papillae
• Posterior 1/3 (pharyngeal surface) has no papillae - mucosa is irregular due to many small nodules of lymphoid tissue = lingual tonsil

Inferior Surface

• No papillae
• Has a single median fold - frenulum of the tongue - continuous with the floor of oral cavity mucosa
• Underlies the lower margin of the midline sagittal septum (which internally separates left and right halves of the tongue)
• On each side of the frenulum = lingual vein
• Lateral to each lingual vein = fimbriated fold

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4. Papillae (Classic Viva)

"All papillae increase the area of contact between the tongue surface and contents of the oral cavity. All EXCEPT filiform papillae have taste buds." - Gray's

Viva key: Only 8 to 12 vallate papillae exist, in a single V-shaped row.

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5. Muscles of the Tongue

• The tongue is completely divided into left and right halves by a median sagittal septum of connective tissue
• Therefore all muscles of the tongue are paired
• Two groups: intrinsic and extrinsic

The Golden Rule (Gray's): "Except for the palatoglossus, which is innervated by the vagus nerve [X], all muscles of the tongue are innervated by the hypoglossal nerve [XII]."

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Intrinsic Muscles (origin and insertion within tongue)

• Working in pairs or one side at a time, intrinsic muscles contribute to precision movements for speech, eating, and swallowing

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Extrinsic Muscles (origin outside tongue, insert into tongue)

Genioglossus is the most important clinically - Gray's states: "If the nerve on one side is not fully functional, the tip of the tongue will point to that side" on protrusion.

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Hyoglossus - The Key Landmark Muscle

• Deep to hyoglossus (between hyoglossus and genioglossus): Lingual artery
• External (superficial) surface of hyoglossus: Hypoglossal nerve [XII] and Lingual nerve (V3)

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6. Vessels

Arterial Supply

• Lingual artery - branch of the external carotid artery, arising at the level of the tip of the greater horn of the hyoid bone
• It forms an upward bend, loops downward and forward, passes deep to hyoglossus
• Travels forward in the plane between hyoglossus and genioglossus to the apex
• Also supplies: sublingual gland, gingiva, oral mucosa of the floor

Venous Drainage

• Deep lingual veins - visible through mucosa on undersurface; travel with hypoglossal nerve on external surface of hyoglossus → drain into internal jugular vein
• Dorsal lingual veins - follow the lingual artery between hyoglossus and genioglossus → drain into internal jugular vein

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7. Innervation

"Innervation of the tongue is complex and involves a number of nerves." - Gray's

General Sensation

Taste (Special Sensory)

Motor

• All tongue muscles → Hypoglossal nerve [XII]
• Palatoglossus only → Vagus nerve [X]

Course of Lingual Nerve (Gray's)

• Originates in infratemporal fossa as branch of V3
• Passes through gap (oropharyngeal triangle) between mylohyoid, superior constrictor, and middle constrictor
• Passes immediately inferior to the attachment of superior constrictor to the mandible
• Continues forward on medial surface of mandible adjacent to the last molar tooth (can be palpated here clinically)
• Loops under the submandibular duct
• Ascends into tongue on the external surface of hyoglossus

Course of Hypoglossal Nerve [XII] (Gray's)

• Leaves skull through hypoglossal canal
• Descends in the neck to just below angle of mandible
• Crosses the external carotid artery, crosses the loop of the lingual artery
• Reaches external surface of lower 1/3 of hyoglossus
• Enters tongue through the oropharyngeal triangle
• C1 fibers hitch a ride on CN XII and leave as:
  • Superior root of ansa cervicalis
  • Thyrohyoid branch (innervates thyrohyoid)
  • Branch to geniohyoid

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8. Lymphatic Drainage

"All lymphatic vessels from the tongue ultimately drain into the deep cervical chain of nodes along the internal jugular vein." - Gray's

• Submental nodes lie inferior to mylohyoid muscles, between the digastric muscles
• Submandibular nodes lie below the floor of the oral cavity along the inner aspect of the inferior margins of the mandible

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9. One-Liner Viva Bombs from Gray's

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