Ultrastructural observations on closure of the soft palate in hamsters

Subcellular events during soft palate closure in hamsters were studied electron microscopically. In the early stages the surface epithelium of the palatal shelves was 2–3 cell‐layers thick and was separated from the underlying mesenchyme by an intact basal lamina. The epithelial cells contained few cytoplasmic organelles and were attached to each other by desmosomes. During further development tonofilaments and lysosomes appeared in the epithelial cells. Prior to fusion the epithelia of the opposing shelves displayed thickening followed by desquamation of the superficial cells. Fusion occurred by means of newly formed desmosomes between the fresh surfaces of the opposing epithelia of the shelves, thereby forming an epithelial seam bounded on each side by the basal lamina. Subsequent thinning and fragmentation of the seam occurred as a result of autophagy, exfoliation, and extrusion of cells through the intercellular spaces. Macrophages appeared at a later stage of soft palate development and removed the cellular debris. At no time during these stages of palatogenesis was there evidence of penetration of the basal lamina on either side of the epithelial seam by the surrounding mesenchyme.