Merging the old skeletal biology with the new. I. Intramembranous ossification, endochondral ossification, ectopic bone, secondary cartilage, and pathologic considerations

Skeletogenesis and chondrogenesis result from a sequence of events involvin g epithelial-mesenchymal interaction, condensation, and differentiation. Ty pes of bone and cartilage formation include: (1) intramembranous ossificati on, (2) endochondral ossification, (3) combined endochondral and intramembr anous ossification, (4) heterotopic bone and cartilage formation, and (5) s econdary cartilage formation. Pathologic conditions with bone and cartilage include: (1) benign and malignant tumors and (2) reactive osseous and cart ilaginous metaplasia.