Mesenchymal fusion of the palatal processes and of heterotypic explants.

Two palatal sheleves were cultured for 3 to 6 h, and palatal shelves and half lips were associated and cultured for 24, 48 or 72 h on an agar culture medium. In all cases an epithelial wall was observed between the two mesenchymes. In homotypical palatal shelf cultures, the medial palatal wall disappears and mesenchymal fusion occurs. The epithelial barrier in palate-lip associations is constituted at first by palatal and labial cells, then purely labial, the medial palatal epithelium undergoing destruction. This labial wall pushed away by the actively growing mesenchyme finally disappears so that the palatal and labial mesenchymes are continuous. This phenomenon is completely different from the mesenchymal fusion and has not the same characteristics.