ABSTRACT
The embryology of the thyroid and parathyroid glands underlies the anatomical position, anatomical variations and congenital conditions of these structures; it is therefore vital for surgery. The thymus also develops from the third pouch. As it descends, the thymus takes the associated para thyroid gland with it, which explains why the inferior parathyroid, which arises from the third pharyngeal pouch, normally lies inferior to the superior gland. A branch of the vagus, the nerve recurs round the arch of the aorta on the left and the subclavian artery on the right. The clinical significance of this is that on the left the nerve has more distance in which to reach the tracheo-oesophageal groove and therefore runs in a medial plane. Synthesis and release of thyroid hormones from the thyroid is controlled by thyroid-stimulating hormone from the anterior pituitary.
