During development of the great vessels, the left sixth aortic arch artery gives rise to the ductus arteriosus and part of the left pulmonary artery. Which adult anatomical relationship is explained by this origin?

• A The vagus nerve crosses anterior to the aortic arch
• B The right recurrent laryngeal nerve loops under the subclavian artery
• C The left recurrent laryngeal nerve loops under the aortic arch near the ligamentum arteriosum ✓
• D The left phrenic nerve passes anterior to the root of the lung

Explanation

In the embryo the recurrent laryngeal nerves hook under the sixth arch arteries. On the right, the distal sixth arch disappears, so the nerve ascends to hook under the fourth arch derivative, the subclavian artery. On the left, the distal sixth arch persists as the ductus arteriosus, dragging the left recurrent laryngeal nerve down so it loops under the ligamentum arteriosum in the adult.

Reference: Langman's Medical Embryology, 14th ed.

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