This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Anatomy
All developed up to the adult size at bih except 
Select and explain. 
A. Mastoid Antrum, B. Tympanic cavity, C. Orbital cavity, D. Ear ossicle
C: Orbital cavity
Answer: C: Orbital cavity 
Explanation: Tympanic cavity, mastoid (tympanic) antrum, ear ossicles and the Internal ear are of adult size in the foetal skull.