No abstract

During the final period of embryogenesis, the nasal pit is clearly apparent in the Carnegie stage 15 embryo, and extends backwards into the oral cavity forming the nasal sac. In the stage 19 embryo of about 7 weeks, abundant epithelial proliferation into the lumen forms the nasal meatal plug. The complete recanalization of this meatal plug occurs in the 16-17 week fetus, and not in the 24th week of fetal life as is generally accepted in textbooks on human embryology. The findings of the present study of the embryology of the anterior nares can well explain the anomalies of the human anterior nares aperture.

No abstract

During the final period of embryogenesis, a funnel-shaped tube continues medially into the mesenchymal tissue forming a curved path. Although this may sound simple, the development occurring during early fetal life is in fact very complex. At first, ectodermal cells proliferate to fill the lumen of the meatus, forming the meatal plug, and then at 10 weeks the bottom of the plug 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. In the 13-week fetus, the disc-like plug begins to show signs of its final destiny; the innermost surface of the plug in contact with the anlage of the malleus is ready to contribute to the formation of the tympanic membrane. In the 15-week fetus, the innermost portion of the disc-like plug 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. In the 16.5-week fetus, the meatus is fully patent throughout its entire length, although the lumen is still narrow and curved. In the 18-week fetus, the meatus is already fully expanded to its complete form.

No abstract