Fig. 9. Right-sided view of avian embryo, near hatching (19 days). This embryo was injected with β-galactosidase-marked retrovirus at 2 days' incubation. The injected area corresponded to deep paraxial mesenchyme at the mesencephalic level (see Fig. 10). The embryo was fixed, stained for the presence of marker, and dissected. The deep blue muscle (which carries the retrovirus) is the dorsal oblique. (Fixman J, Wahl C, Noden D: Unpublished data.)