4 Fourth pharyngeal pouch ---dorsal portion: forms superior parathyroid gland ventral portion; degenerates 5 Fifth pharyngeal pouch gives rise to the ultimobranchial body, immigrate into thyroid and differentiate into parafollicular cells 甲状腺原基 下甲状旁腺原基 上甲状旁腺原基④ Fourth pharyngeal pouch: ---dorsal portion: forms superior parathyroid gland ---ventral portion: degenerates ⑤ Fifth pharyngeal pouch: ---gives rise to the ultimobranchial body, immigrate into thyroid and differentiate into parafollicular cells