Fig. 5. The foregut endoderm patterns the neural crest-derived skeleton. (A) Transplantation of endodermal zone II from quail into stage-matched chick neurula. (B,C) Sections of the operated embryonic day (E) 6 host after detection of quail cells [quail cell-specific antibody against a perinuclear antigen (QCPN), brown] and cartilage staining (Alcian Blue). (B) Laterally engrafted endodermal cells have induced ectopic differentiation of chondrogenic cells, which all derive from host mesectoderm (see enlargement in C). (D) Bilateral grafting of quail endodermal stripe (II) implanted ventrally into a stage-matched chick embryo. (E) At E9, the host shows an additional lower beak apparatus (lb^*) interposed between the endogenous upper (ub) and lower (lb) components of the host bill. (F) This supernumerary structure is accompanied by an additional Meckel's cartilage (Mc^*) (Alcian Blue staining). Reproduced, with permission, from Couly et al. (Couly et al., 2002). A, articular; Ey, eye; NaCa, nasal capsule; Q, quadrate.