Rathke’s pouch is located at a triple boundary. (a) Whole-mount LacZ staining of an R26R-Sox17-Cre E10.5 mouse embryo showing the anterior limit of the endoderm (red arrowhead) and the posterior border of Rathke’s pouch (blue arrowhead); endobuccal view of the oral roof. (b) Anterior limit of the endoderm in the mid-sagittal plane at E10.5 (arrowhead), LacZ staining, R26R-Sox17-Cre mouse embryo. (c) Posterior limit (arrowhead) of the neural crest-derived mesoderm in the mid-sagittal plane at E12.5, corresponding to the location of the closing buccohypophyseal canal, in an R26R-Wnt1-Cre mouse embryo. (d) Anterior end of the notochord (arrowhead), eosin staining, E10.5, wild-type mouse embryo ant, anterior; post; posterior; RP, Rathke’s pouch.