With the object elucidating the fusion mechanism of the rats secondary palate, the following experiments were performed with rat embryos of 15 days 12 hours and 16 days 12 hours of age.
1) Pairs of 15-day 12-hour embryos, separated from the neighbouring tissue were placed side by side to be incubated at 72 hours and 96 hours.
2) Pairs of lateral palatal shelves of 15-day 12-hour embryo, with a portion of the basis cranii attached to each, were together incubated for 48 hours.
3) Pairs of lateral palatal shelves of 16-day 12-hour embryo, with a portion of the basis cranii attached to each, were together incubated for 48 hours.
4) Pairs of lateral shelves of 16-day 12-hour embryo with a foreign body-Milllpore Filter-inserted between each pair at an anterior 1/3, which had already been fused, were incubated for 72 hours to observe the development of the fusion.
5) Pairs of lateral palatal shelves of 15-day 12-hour embryo, with each two parts shifted one another along the the median lines, were incubated for 72 hours and 96 hours.
and the fusion processes in these experiments were histologically observed with the following results.
a) In experiment 1, mesenchymal transmigration occured in all length of lateral palatal shelves.
b) In experiments 2 and 3, epithelial fusion was confirmed to progress continuously both anteriorly and posteriorly frcm the point of the primary joining, accompanied by stratification of epithelial cells.
c) In experiment 4, mesnchymal transmigration occurred except in the part where the contact of the two lateral palatal shelves was prevented by the insertion of a Millipore Filter. Then in experiments 3 and 4, even when continuous joining of lateral palatal shelves was inhibited, fusion took place at the posterior end.
d) In experiment 5, mesenchymal transmigration occurred despite the horizontal shift of the two shelves on the surface of contact.
f) From these results, the fusion mechanism of the lateral shelves of the rat embryo can be suggested a concrescence.
g) In the end, a clinical case of the secondary palate showing a particular morphology of median fissure was examined, and its genesis was discussed.
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