Fig. 11. Hh signaling specifies the ability of the stomodeum to condense neural crest cells on its roof. (A) Schematic of a 10 hpf embryo. Shh (yellow) secreted from the ventral presumptive brain signals to stomodeum precursors (red) in the anterior ectoderm. Premigratory neural crest cells (green) are distant from the Hh source. (B) Later in development, starting at 21 hpf, the stomodeum signals to neural crest cells through an unknown mechanism, causing anterior craniofacial neural crest cells to condense.