Fig. 6. Analysis of the primary spongiosa in chimeric embryos. Smo^n/n cells fail to contribute to the primary spongiosa in chimeric embryos (A,B) whereas Smo^n/+ cells contribute extensively (C). Longitudinal sections of the tibia at E17.5 are stained with H&E. Smo^n/n or Smo^n/+ cells are stained blue as a result of the expression of ß-galactosidase. The boxed region in A is shown at a higher magnification in B. Asterisks denote the blood vessels. Arrows in B point to occasional Smo^n/n cells in the marrow cavity.