Fig. 8. Functional domains and relationships of the Pbx1 and Hox genes in axial and appendicular skeletal morphogenesis. (A,B) Coloured lines indicate the anatomical regions affected by mutations in the Pbx1 or Hox genes (paralog groups 9-13 in the limb and 2-4 in the ectomesenchymal component of the branchial arches). In the embryonic limb, Meis protein expression is spatially coincident with Pbx1-dependent regions and unperturbed in a Pbx1 mutant background. B is adapted from Couly et al. (Couly et al., 1996). (C) Schemata depicting chondrocranial morphologies in wild-type, Pbx1^-/- and Hoxa2^-/- embryos at E16. The latter represents authors’ interpretation of Rijli et al. (Rijli et al., 1992). Although not phenocopies, both Pbx1^-/- and Hoxa2^-/- mutants exhibit mandibular arch-like morphologies in the hyoid arch (BA2). Dark blue indicates BA1 structures, yellow, wild-type BA2 structures, and red, mutant BA2 structures at E16. Lateral views, upper panels; basal views, lower panels. ala temporalis, at; greater horn of hyoid, gh; hyoid body, hb; incus, in; lesser horn of hyoid, lh; malleus, ma; Meckel’s cartilage, MC; styloid process, sp; stapes, st.