Embryology Pharyngeal Pouches USMLE Review
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Explanation:
The epithelial lining of the second pharyngeal pouch buds into the mesenchyme to form the palatine tonsil. Part of the pouch remains in the adult as the tonsillar fossa.
It is important to review the other choices since pharyngeal pouch derivatives are typically tested on the USMLE Step 1:
The first pharyngeal pouch (choice A) develops into the middle ear cavity and eustachian tube. 
The third pharyngeal pouch (choice C) develops into the thymus and the inferior parathyroid glands.
The fourth pharyngeal pouch (choice D) gives rise to the superior parathyroid glands. Recall that abnormal development of the 3rd and 4th pouches leads to DiGeorge syndrome and results in hypocalcemia as well as abnormal cellular immunity and consequent susceptibility to viral and fungal illnesses.
The fifth pharyngeal pouch (choice E) gives rise to the C cells of the thyroid gland. These cells secrete calcitonin–a hormone that lowers serum calcium.
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