This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anatomy
[{'content': 'Pisiform is which type of bone: \nSelect and explain. \nA. Pneumatic bone, B. Sesamoid bone, C. Accessory bone, D. Long bone', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The pisiform is a sesamoid bone, with no covering membrane of periosteum. It is the last carpal bone to ossify.\xa0\nThe pisiform bone is a small bone found in the proximal row of the wrist (carpus).\xa0\nIt is situated where the ulna joins the wrist, within the tendon of the flexor carpi ulnaris muscle.', 'role': 'assistant'}]