Length of external auditory meatus is ?
Ans. is 'd' i.e., 24 mm External auditory canal (External acoustic meatus) External auditory canal is a 'S' shaped canal with length of 24-25 mm and it is divided into two pas :? 1) Cailagenous pa It forms outer/lateral 1/3 (8mm) of the external auditory canal. It has two fissures / deficiencies in the anterior pa called fissure of santorini through which parotid or superficial mastoid infection can appear in the canal and vice versa. Skin covering it is thick and has ceruminous glands (modified apocrine sweat glands), pilosebaceous glands and hair. Since hair is confined to cailaginous pa, furuncles are seen only in the outer third of the canal. 2) Bony pa It forms inner/medial 2/3 (16 mm) of external auditory canal. Skin lining the bony pa is thin and is devoid of hair and ceruminous glands. Isthmus is the narrowest poion of bony canal and is 5 mm lateral to tympanic membrane. Foreign bodies get lodged in isthmus are difficult to remove as it is the narrowest pa. `Foramen of Huschke' is a deficiency present in antero-inferior pa of bony canal in children upto 4 years of age, permitting infection to and from parotid.
12mm
16mm
20mm
24mm