Which cranial nerve is associated with both the fourth and fifth pharyngeal arches?

• A. CN V
• B. CN VII
• C. CN IX
• D. CN X

Answer: (D)

Arches 4 and 6 share their motor supply from the vagus nerve. In human development, the fifth arch is not really present as a distinct structure, so the nerve linked to arches 4 and 5 is effectively the vagus. Each arch has a specific cranial nerve pairing: arch 1 with CN V, arch 2 with CN VII, arch 3 with CN IX, and arches 4 and 6 with CN X. The vagus nerve provides the muscles that arise from these arches, including the pharyngeal constrictors and most intrinsic laryngeal muscles (via its superior and recurrent laryngeal branches). That’s why CN X is the correct association for both the fourth and the (fifth, effectively absent) arches.