In adults, the eardrum is 2.5 to 3.5 centimeters inside the ear, while in children, the eardrum is 1.5 to 2 cm.
The external auditory canal starts from the bottom of the eardrum cavity and ends at the tympanic membrane inward, consisting of a cartilage part and a bone part, with a slight S-shape curvature. The outer 1/3 of the external auditory canal in adults is the cartilage part, and the inner 2/3 is the bone part. There are two narrower parts of the external auditory canal, one is the junction of the bone part and the cartilage part, and the other is the bone part about 0.5cm away from the tympanic membrane, which is called the isthmus of the external auditory canal.
The outer section of the external auditory canal is inward, forward and slightly upward, the middle section is inward and backward, and the inner section is inward, forward and slightly downward. Sometimes, when examining the external auditory canal, the curved and narrow part of the canal may be mistaken for the eardrum. When it is necessary to examine the deeper part of the ear canal or the eardrum, the doctor often lifts the auricle back upward so that the external auditory canal is in a straight line.
The entire length of the external auditory canal is 2.5 to 3.5 cm in adults and 1.5 to 2 cm in children, starting at the mouth of the external auditory canal and ending at the eardrum.