During the eighth to tenth week, the cells of the duct normally begin growing inwards and fill the previously hollow tube, beginning from the inferior end. This inferior end of the duct will then become the pyramidal lobe of the thyroid gland. The dividing cellular cords of the tubular duct become the isthmus and lateral lobes of the gland to complete the formation of the rest of the gland.
During weeks eight to ten, the cells in the duct begin growing inwardly and fill the hollow tube that was previously empty, starting from the lower end. This lower end of the duct will become the pyramidal lobe of the thyroid gland. The dividing cellular strands of the tubular duct transform into the isthmus and lateral lobes to complete the formation of the rest of the gland.