This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
Bone does not present at bih is 
Select and explain. 
A. Malleus, B. Incus, C. Stapes, D. Petrous temporal
D: Petrous temporal
Answer: D: Petrous temporal 
Explanation: *Malleus and incus - derived from the dorsal end of Meckel&;s cailage *Stapes - from the dorsal end of the cailage of the second pharyngeal arch. *The ear ossicles ossify fully in the 4th month of IUL - 1st bones in the body to do so. *The mastoid process is not present at bih and stas developing at end of the first year and reaches its adult size at pubey. *Mastoid antrum is an air-filled sinus within petrous pa of temporal bone. Development of the mastoid air cell system doesn't occur until after bih. Reference: I B Singh&;s Embryology, 10th edition, pg 368