This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Head and neck, Subject name: Anatomy
Thymus develops from 
Select and explain. 
A. I Pharyngeal pouch, B. II Pharyngeal pouch, C. III Pharyngeal pouch, D. IV Pharyngeal pouch
C: III Pharyngeal pouch
Answer: C: III Pharyngeal pouch 
Explanation: Pharyngeal pouchDerivativesDorsal ends of I and II pouches form --Tubotympanic recessThe proximal pa of tubotympanic recess gives rise to auditory tube.Distal pa gives rise to tympanic cavity and mastoid antrum. Mastoid cellsdevelop at about 2 years of ageVentral pa of II pharyngeal pouchEpithelium covering the palatine tonsil and tonsillar crypts, lymphoid tissueis mesodermal in originIII Pharyngeal pouchThymus and inferior parathyroid gland or parathyroid III.IV Pharyngeal pouchSuperior parathyroid or parathyroid IVV Pharyngeal pouch (ultimobranchial body)Parafollicular or 'C' cells of the thyroid glandRef: Chaurasia; Volume 3; 6th edition; Page no: 30