Which pharyngeal membrane is the only one out of the four to form a distinct structure?

• A. First pharyngeal membrane
• B. Second pharyngeal membrane
• C. Third pharyngeal membrane
• D. Fourth pharyngeal membrane

Answer: (A)

Pharyngeal membranes are transient partitions between each pharyngeal groove and its corresponding pharyngeal pouch. Of the four, only the first membrane forms a distinct adult structure—the tympanic membrane. This membrane comes to separate the external ear from the middle ear at the boundary between the first groove and the first pouch. Its outer surface is derived from ectoderm of the first groove, its inner surface from endoderm of the first pouch, with a connective tissue layer in between from neural crest cells. The other membranes do not persist as separate structures; they disappear as the arches and pouches develop and fuse, so they don’t yield distinct organs of their own.