Development of the tongue and thyroid

First pharyngeal arch

Third Branchial arch

Second pharyngeal arch

4th arch

proliferation of mesoderm in floor of pharynx

Median tongue bud (tuberculum impar)

Distal tongue buds (lateral lingual swellings)

rapidly over grow tuberculum impair

anterior 2/3 of tongue

mesoderm

hypobranchial/hypopharyngeal eminence

mesoderm

copula

hypobranchial eminence covers copula

posterior 1/3 of tongue

contributes to

forms root of tongue and epiglottis

whole tongue

dorsal endoderm of tongue

Thyroid diverticulum

descends ventral/anterior to hyoid and larynx

Thyroglossal duct is formed opening into foramen caecum

Thyroid gland over upper trachea

Thyroglossal duct disintegrates

foramen caecum remains as a small pit on dorsal tongue

in some individuals an inferior remnant remains

forms pyramidal lob connecting isthmus of thyroid to hyoid bone by fibrous tissue or muscle