The markedly variable position of the INFERIOR parathyroid glands, ranging from the angle of the jaw to the anterior mediastinum, is explained by which embryological fact?

• A They arise from the fourth pharyngeal pouch and migrate a short distance
• B They arise from the ultimobranchial body and fuse with the thyroid lobes
• C They arise from neural crest cells that migrate along the carotid sheath
• D They arise from the third pharyngeal pouch and descend with the thymus ✓

Explanation

Inferior parathyroids arise from the dorsal wing of the third pharyngeal pouch together with the thymus. Their long descent alongside the thymus explains their wide variability in final position, including intrathymic and mediastinal locations, and why supernumerary glands may sit in the thymic fat. Superior glands arise from the fourth pouch, descend only slightly, and therefore have a far more constant position near the cricothyroid junction, often within the pretracheal fascia posterior to the thyroid.

Reference: Schwartz's Principles of Surgery, 11th ed.

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Written and medically reviewed by the StethoPrep medical team.