<prompt> Length of external auditory meatus is -12mm16mm20mm24 mm  <response>: Ans. is d i.e., 24 mm External auditory canal tExternaJ acoustic meatuso External auditory canal is a S shaped canal with length of 24-25 mm and it is divided into two partsCartilagenous partIt forms outerlateral 13 8mm of the external auditory canal. It has two Assures deficiencies in the anterior part 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 cartilaginous pan, furuncles are seen only in the outer third of the canal.Bony partIt forms innermedial 23 16 mm of external auditory canal. Skin lining the bony part is thin and is devoid of hair and ceruminous glands. Isthmus is the narrowest portion 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 part. Foramen of Huschke is a deficiency present in antero-inferior part of bony canal in children upto 4 years of age, permitting infection to and from parotid. 