Mouse adult ruga pattern and its visualization in the fetus by in situ hybridization against Shh gene. (A) The roof of the oral cavity of an adult mouse showing the palatal ridges (rugae palatinae) on the hard palate. (B) Mouse rugae pattern with numbering used in this study. Note that ruga 7b was called 8b in other studies (Peterkova et al. 1987; Charles et al. 2007). (C) In ED16.0 fetus, Shh gene expression pattern (as seen by whole-mount in situ hybridization) prefigures the adult ruga pattern. (D) Sagittal section through the same embryo as in C, showing Shh expression in the epithelium at the tip of rugae (see magnification in the low left corner). The absence of Shh signal in the rugae 1–4 can be explained by its discontinuity in the anterior rugae at this stage (see C).