This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anatomy of External Ear & Pinna, Subject name: ENT
Length of external auditory canal is 
Select and explain. 
A. 20 mm, B. 22 mm, C. 24 mm, D. 15 mm
C: 24 mm
Answer: C: 24 mm 
Explanation: Ans. c (24 mm). (Ref. PL Dhingra Diseases of ENT 2nd/pg.3)EXTERNAL AUDITORY CANAL# It starts at the external auditory meatus and ends at the tympanic membrane, where a bony structure (bony outer attic wall at tympanic membrane, where ECA ends) projects, called scutum.# It is almost S shaped curved canal of about 24 mm length.# It has:- outer cartilaginous part (2/3rd) and- inner bony part (l/3rd).# It is directed upwards, backwards and medially in outer part and downwards, forwards and medially in inner part.# The periosteum is very firmly adherent in EAC and hence even a minor infection like a furuncle is extremely painful.