During descent, which structure attaches to the dorsal surface of the thyroid?

• A. Superior parathyroid
• B. Inferior parathyroid
• C. Thymus
• D. Ultimobranchial body

Answer: (A)

The key idea is how structures from the pharyngeal pouches migrate with the developing thyroid. The superior parathyroid glands come from the fourth pharyngeal pouch and migrate so they rest on the posterior (dorsal) surface of the thyroid gland as the thyroid descends. This placement on the back of the thyroid is a distinctive feature of their final position. In contrast, the inferior parathyroids originate from the third pouch and descend with the thymus toward the lower pole of the thyroid, thymus itself travels to the superior mediastinum, and the ultimobranchial body fuses with the thyroid tissue but doesn’t establish that dorsal attachment. So, the structure that attaches to the dorsal surface of the thyroid during descent is the superior parathyroid.