Question

The length of the external auditory meatus is?

• A. 12 mm
• B. 16 mm
• C. 20 mm
• D. 24 mm

Hint:

Add the cartilaginous outer third (about 8 mm) to the bony inner two-thirds (about 16 mm).

Answer 1

The Correct Option is D

Step 1: The external auditory canal (external acoustic meatus) is an S-shaped canal extending from the concha to the tympanic membrane, with a length of about 24 to 25 mm. Hence the answer is 24 mm.

Step 2: It is divided into two parts. The outer or lateral one-third is the cartilaginous part, about 8 mm long, lined by thick skin with hair, ceruminous glands, and pilosebaceous glands; furuncles occur only here.

Step 3: The inner or medial two-thirds is the bony part, about 16 mm long, lined by thin skin without hair or ceruminous glands. The isthmus, the narrowest part, lies about 5 mm lateral to the tympanic membrane.

Step 4: Adding the cartilaginous 8 mm and bony 16 mm gives roughly 24 mm, so the shorter options are incorrect.