:  Most cells in mesenchymal condensations that form endochondral bone become chondrocytes; cells at the outer edges of the condensations, however, become perichondrial cells with distinct properties and functions. Some perichondrial cells become osteoblasts that populate both the future cortical and trabecular bone; others probably become chondrocytes. Perichondrial cells both send signals to the underlying growth cartilage and receive signals from the cartilage. Here I illustrate briefly examples of the complicated interactions between the perichondrium and the underlying growth cartilage.