Length of external auditory meatus is -

Ans. is 'd' i.e., 24 mm External auditory canal tExternaJ acoustic meatus)o External auditory canal is a 'S' shaped canal with length of 24-25 mm and it is divided into two partsCartilagenous partIt forms outer/lateral 1/3 (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 inner/medial 2/3 (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.