part of part of develops from develops from tissue endocrine system chordate pharynx primordium thyroid primordium The initial thyroid precursor, the thyroid primordium, starts as a simple midline thickening and develops to form the thyroid diverticulum. This structure is initially hollow, although it later solidifies and becomes bilobed. The 2 lobes are located on either side of the midline and are connected via an isthmus. Note that we follow EHDAA2 in dividing this into endoderm and mesenchyme. In this ontology we place the broad developmental relationship at this level, and include specific relationships to the pharyngeal endoderm at the level of the endoderm EMAPA:16361 XAO:0000444 AAO:0011106 EHDAA2:0002033 NCIT:C34312 UBERON:0003091 In all vertebrates the thyroid arises from the ventral aspect of the second pouch BTO:0004709 UMLS:C1519512 thyroid primordia Portion of tissue part of the pharyngeal endoderm that is fated to become thyroid follicle[ZFIN:curator]. TAO:0001081 EHDAA:952 ZFA:0001081 endoderm-derived structure pharyngeal pouch 2