Anteroposterior limits of expression of Shox2 , Meox2 and Tbx22 genes coincide with ruga 8 in the mouse. Whole mount in situ hybridization for Shh, Shox2, Meox2 and Tbx22 were performed on dissected mouse upper jaws at three embryonic stages (ED12.5, ED13.5 and ED14.0, embryos of similar weight classes) (A), and were followed by sectioning, and counterstaining with nuclear red (except for Shox2 and Meox2 at ED12.5) (B). Rugae are numbered (with brackets when damaged by dissection). The white arrowhead points the anterior limit of the palatal shelf and the black arrowhead points ruga 8. The dashed line indicates where the very posterior part of the shelf was damaged by dissection.