The vertebrate pharyngeal arches and their derivatives. (A) Lateral view of an amniote embryo, showing the characteristic bulges of the pharyngeal arches number 1 to 4 from anterior. The pouches intercalate between the arches. The position of the eye and ear are shown. (B) Schematic of a transverse section through the arch region, showing the constituent tissues: ectoderm, dark blue; endoderm, green; neural crest, pale blue ; mesoderm, purple.