Jaw muscle precursors express the eng2 and eng3 genes. Parasagittal sections of 32 h embryos were hybridized with probes for the eng1 (A), eng2 (8), or eng3(C) genes. Precursors of the jaw muscles (arrows) are indicated. The signal around the eye in each panel is caused by the pigment epithelium of the retina rather than to specific hybridization as shown in unhybridized control sections. Scale bar, 50 μm.