第1咽囊 甲状舌管动 第2咽囊 扁桃体窝 甲状 第3咽囊 下甲状旁腺原基 第4咽囊 上甲状旁腺原基 后魑体 development of thyroid gland thyroid primordium by the 4 th week endodermal proliferation of the floor of primitive pharynx, then descends in front of the primitive pharynx as a bilobed diverticulum thyroglossal duct: a narrow canal connecting primitive pharynx with thyroid primordium by the 6th week, becomes solid and disappears*development of thyroid gland ---thyroid primordium: by the 4th week, endodermal proliferation of the floor of primitive pharynx, then descends in front of the primitive pharynx as a bilobed diverticulum ---thyroglossal duct: a narrow canal connecting primitive pharynx with thyroid primordium, by the 6th week, becomes solid and disappears