Part of “CHAPTER 48 – MORPHOLOGY OF THE PARATHYROID GLANDS“

The parathyroid glands develop from the third and fourth pharyngeal (branchial) pouches (see Chap. 53, Fig. 53-4). The third pharyngeal pouch, containing the thymus and parathyroid tissue, migrates downward until the embryo is 18 mm in size, at which time the two inferior parathyroids attain their normal location at the lower poles of the thyroid.1 The fourth pharyngeal pouch is the source of the two upper parathyroid glands, which remain attached to the upper poles of the thyroid.1