Fig. 1. Somitic muscle progenitor specification occurs prior to induction of Scx in the sclerotome. Whole-mount in situ hybridization at E10.5 (A-D) for Scx (A), Myf5 (B), Myod1 (C) and Fgf4 (D). (E-L) Section in situ hybridization for Scx (E,I), Myf5 (F,J), Myod1 (G,K) and Fgf4 (H, L), on alternate sagittal (E-H) or frontal (I-L) sections, through somites of E10.5 embryos. Blue arrows indicate forelimb buds; purple arrows, hindlimb buds; green arrows, branchial arches. Black arrows in E-H indicate onset of expression.