(A-B) ROR2 (A) and WNT5A (B) mRNA expression in facial primordia that will form the upper and lower beak from HH29 short and medium beak pigeon embryos. Each individual embryo is displayed in a different color. (C-H) Whole-mount in situ hybridization for ROR2 (C-E) and WNT5A (F-H) in medium beak pigeon embryos at HH21, HH25, and HH29. ROR2 is broadly expressed in facial primordia at all stages. WNT5A is strongly expressed in the FNP and at the lateral edges of the MXP and LNP, with increased expression at the edge of the MDP at HH29. Letters indicate embryonic tissues/structures: e=eye, fnp=frontonasal prominence, l=lateral nasal prominence, mdp=mandibular prominence, mxp=maxillary prominence.