Fig. 7. Analysis of bone formation in the perichondrium following activation of Ihh signaling. (A-H) In situ hybridization using ³⁵S-labeled riboprobes on longitudinal sections of the tibia at E16.5; probes and genotypes as indicated. Signals are shown in red and the sections are counterstained with Toluidine Blue. H, hypertrophic chondrocytes; M, marrow cavity. Asterisks denote the perichondrium in which Ptc1 or Cbfa1 are up-regulated.