Final answer:
The bone described as a thin, flat plate with another perpendicular plate is the palatine bone, which forms part of the hard palate in the skull.
Step-by-step explanation:
The bone that feels like a small, thin, flat plate in one plane and then has an even smaller thin, flat plate perpendicular to the main plate is d. Palatine bone. The palatine bone is an irregularly shaped bone that contributes to the lateral walls of the nasal cavity and the medial wall of the orbit. Its largest region is the horizontal plate, which combines with its counterpart from the other side to form the posterior quarter of the hard palate. This structure can be best observed in an inferior view of the skull and hard palate, demonstrating the bone's unique two-plane shape.