Embryological Development of the Thyroid ΓÇô 7 weeks
By the seventh week of foetal development, the thyroid is located at the level of the developing trachea as the pharynx grows anteriorly (Fig. 15.3). The gland now has two lateral lobes connected by a narrow isthmus. Thyroid follicles develop at this stage. Cells of the ultimobranchial body are incorporated into the developing thyroid and give rise to the parafollicular or C-cells which then produce calcitonin.
