This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Joints, Subject name: Anatomy
Hardest bone of the body is? 
Select and explain. 
A. Head of humerus, B. Calcaneum, C. Tibial condyle, D. Osseus labyrinth
D: Osseus labyrinth
Answer: D: Osseus labyrinth 
Explanation: Ans. D Osseus labyrinthRef: Gray's Anatomy, 41st ed. pg. 644* Osseous labyrinth is considered as hardest bone of the body. It is embedded in petrous part of temporal bone, which is also known as "rock bone".* American edition of British encyclopedia states: "The labyrinth of the ear is formed of cochlea, 3 semicircular canals and a small cavity known as vestibulum into which cochlea and semicircular canal opens. These parts are formed of the hardest bone in body, almost equal in solidity to ivory and petrous portion of temporal bone.