Abstract
From the observation on palatal region of human embryos aged 5-11 weeks, the author summarised the results as follows.
1) In the tip of palatal process and the lower surface of nasal septum during the secondary palate formation, hypertrophy of the covering, disarrangement of the epithelial cells and disappearance or discontinuity of the basement membrane were observed.
2) PAS positive substances (chiefly consisting of flycogen) were already present in primary oral mucous membrane of fetus at the stage of five weeks. Covering flat epithelium appeared as the palatal processes took horizontal position.
3) At the critical period of palatal formation, following two points were significant.
a. The epithelium at the tip of palatal process invaginated into mesenchymal tissue prior to contact, and the invaginated cell mass was resemble to the form of epithelial peal.
b. In the median portion of lower surface of nasal septum, covering flat epithelial cell appeared and the previous epithelial cells were replaced by them.
4) Though the covering flat epithelium might take part during formation of epithelial pearl in the region of fusion, these cells could not be clearly found in the epithelial pearl.
5) The epithelium at the tip of palatal process was composed of oral and nasal epithelium. The two epithelium assumed to be overlapped. The superficial layer was derived from that of oral epithelium and deep layer from that of nasal epithelium.
6) From the findings mentioned above, it may be possible to say that the specific eptihelial cell changes in the region of fusion bring about not only in the rodents, but in the human embryos.
