Fig. 4. Mesenchymal expression of Fgf10 is decreased, while Mfh1, Hrt1 and Tbx1 appear normal in Fgf8^H/– mutants. Views of the pharyngeal arch area, head is at the top. Arches are numbered in the controls. (A) Mfh1, (B) Hrt1, (C) Tbx1 and (D,E) Fgf10 expression in E9.5 and E10.5 control and mutant embryos. (E) Note the markedly decreased signal in the pharyngeal arches, including area of the developing fourth arch and putative secondary heart field, although expression in limb bud and ototcyst is relatively intact.