Pharyngeal membranes are formed at the intersection of which two structures?

• A. Pharyngeal pouches and pharyngeal clefts.
• B. Pharyngeal arches and pharyngeal pouches.
• C. Pharyngeal arches and pharyngeal clefts.
• D. Pharyngeal membranes with the skin.

Answer: (A)

Membranes form at the interface where the endodermally lined pharyngeal pouch meets the ectodermally lined pharyngeal cleft, with intervening mesenchyme. This boundary creates the pharyngeal membrane, a thin sheet that, for example, contributes to the tympanic membrane at the boundary of the first pouch and first cleft. The pharyngeal arches themselves are the surrounding frameworks that give rise to bones, muscles, and nerves, not the membranes. Thinking in terms of inner pouch lining meeting outer cleft lining makes the idea clear: the membrane comes from the contact of pouch and cleft, not from arches with pouches or clefts, or from skin elsewhere.