Editing Thyroid (section)

=== Median thyroid precursor ('anlage') ===

*** Forms from the primitive pharynx at G2
*** Appears as an epithelial proliferation in the floor of the pharynx between the tuberculum impar and copula, arising at the level of the second pharyngeal arch, between the first and second pharyngeal pouch
*** Descends towards the primitive heart, becoming a bilobed diverticulum with a median tubal structure called the thyroglossal duct, which keeps the structure connected to the tongue
*** Thyroglossal duct becomes a solid structure in the 5th week, after which it fragments and disappears, leaving the foramen caecum at the base of tongue superiorly, and the pyramidal lobe inferiorly (when present)
*** Thyroid continues to descend to its final position anterior to the trachea by the 7th week
*** Cells derived from median thyroid precursor arrange to form follicles and produce thyroid hormone by the 10th week of gestation