At the fourth week of embryonic life, the development of 4 branchial or pharyngeal clefts form, resulting in the formation of 5 ridges known as the branchial or pharyngeal arches which contribute to the formation of various structures of the head, the neck, and the thorax. As the fetus continues developing, the second arch (choice D) grows caudally, to cover the third and fourth arches. The buried clefts become ectoderm-lined cavities, which normally involutes around the 7th fetal week. Failure of a portion of the cleft to involute entraps remnants, which form an epithelium-lined cyst, with or without a sinus tract to the overlying skin.

Aortic Arch Vascular derivatives

First -> part of maxillary artery

Second -> Hyoid and stapedial arteries

Third -> Common carotid artery, proximal internal carotid artery

Fourth -> on left -> aortic arch; on right -> proximal Rt. subclavian artery

Sixth -> proximal pulmonary arteries; on left -> ductus arteriosus