During development of the pharyngeal apparatus, most pharyngeal clefts are obliterated by overgrowth of mesenchyme from the second arch. Which adult structure is derived from the first pharyngeal cleft?
- A External acoustic meatus ✓
- B Tympanic cavity
- C Palatine tonsillar fossa
- D Eustachian tube
Correct answer: A. External acoustic meatus
Explanation
The external acoustic meatus develops from the first pharyngeal cleft, the only cleft that persists as a surface structure. The remaining clefts are buried by proliferation of the second arch mesenchyme, forming the cervical sinus. The tympanic cavity and eustachian tube come from the first pharyngeal POUCH, not a cleft, which is the distinction examiners test. The tonsillar fossa relates to the second pouch.
Reference: Langman's Medical Embryology, 14th ed.
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