Fig. 4. Histological analyses of palate development in Mn1^-/- mutants at late stages. (A,B) At E16.5, the palatal shelves in Mn1^-/- mutant embryos were still vertically oriented. In addition, the palatal shelves appeared to be significantly diminished in size in the middle to posterior regions (B). (C,D) At E18.5, although the palatal shelves in the anterior region in the Mn1^-/- mutant mice were partially elevated (C), the middle and posterior regions of the palatal shelves were further retarded and retracted into the maxillary processes (D). Arrows in B and D indicate the upper first molar tooth germs. p, palatal shelf; t, tongue.