Template:External Auditory Meatus Timeline table

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External Auditory Meatus Timeline
Period Week Description
Embryo week 8 Funnel-shaped tube continues medially into mesenchymal tissue, forms a curved path.
Fetus (first trimester) week 9 Ectodermal cells proliferate, fill the meatus lumen and form the "meatal plug".
Fetus (first trimester) week 10 Meatal plug bottom extends in a disc-like fashion, so that in the horizontal plane the meatus is boot-shaped with a narrow neck and the sole of the meatal plug spreading widely to form the future tympanic membrane medially. At the same time, the plug in the proximal portion of the neck starts to be resorbed.
Fetus (second trimester) week 13 Meatal plug disc-like, innermost surface in contact with the primordial malleus, contributes to formation of tympanic membrane.
Fetus (second trimester) week 15 Meatal plug innermost portion splits, leaving a thin ectodermal cell layer of immature tympanic membrane. The neck of the boot forms the border between the primary and secondary meatus, and is the last part to split.
Fetus (second trimester) week 16.5 The meatus is fully patent throughout entire length. Lumen is still narrow and curved. Epithelium cornification commences.
Fetus (second trimester) week 18 The meatus is now fully expanded to its complete form.
Links: outer ear | hearing | timeline     Reference[1]
  1. Nishimura Y & Kumoi T. (1992). The embryologic development of the human external auditory meatus. Preliminary report. Acta Otolaryngol. , 112, 496-503. PMID: 1441991