Abstract
Ultrastructural findings of secondary palatogenesis were investigated from days 14.0 to 17.5 in the fetuses of Wistar Imamichi rats by scanning electron microscopy.
The results are summarized as follows.
1. On day 15.0 when the palatal shelf began to bulge vertically, a distinct boundary was found between the lateral cobblestone shaped cells and the medial flattened cells along the ridge of the shelf.
2. On day 16.3 cobblestone shaped cells began to appear on the anterior third of the future nasal side of the shelf.
3. The boundary between the cobblestone shaped cells and the flattened cells translocated gradually from the future oral to the future nasal surface of the shelf during the reorientation of the palatal shelf. We are of the opinion that the epithelial movement interacts with proliferation of the underlining connective tissue. We assume that a gradual intrinsic force plays a very important role in the reorientation of the palatal shelves.
4. On day 16.6 just before the middle portion of the shelf came into contact all flattened cells on the nasal side of the shelf were replaced by cobblestone shaped cells. The cobblestone shaped cells began to degenerate into the form of cauliflower on the tip of the medial edge. This degeneration advanced on not only the oral side but also the nasal side of the shelf.
5. On day 16.6 the convex raised cells, which were smaller than the cobblestone shaped cells, were newly formed on the corner between the cobblestone shaped cells and flattened cells on the nasal base of the shelf. Many cilia and microvilli covered the convex raised cells.
