Tongue Development
  •  Anterior 2/3 of tongue
    • derived from 1st branchial arch
      • sensation: lingual branch of CN V3
      • taste: chorda tympani branch of CN VII
  • Posterior 1/3 
    • derived from 3rd and 4th branchial arches
      • sensation and taste: CN IX
      • extreme posterior sensation and taste: CN X
  • Motor innervation
    • all muscles of tongue: CN XII except palatoglossus (CN X)
    • muscles of tongue are derived from myoblasts originating from the occipital somites
Thyroid Development
  •  Thyroid diverticulum 
    • develops from endodermal lining of foregut
    • appears from the midline of the floor of the primitive pharynx
    • descends into the neck maintaining a connection to the tongue through the thyroglossal duct
      • thyroglossal duct degenerates during development
        • may remain as pyramidal lobe of thyroid
        • foramen cecum: remnant of thyroglossal duct
  • Thyroglossal duct cyst 
    • persistent thyroglossal duct forming a cyst in midline of neck near hyoid bone
      • other location is at base of tongue: lingual cyst
    • cyst moves during swallowing
  • Ectopic thyroid tissue 
    • failure of migration downward can result in ectopic thyroid tissue forming anywhere along the thyroglossal duct's path
    • tongue is the most common site of ectopic thyroid tissue 

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