The document discusses skeletal development and growth. There are three main processes of skeletal growth at the cellular level: hypertrophy, hyperplasia, and extracellular matrix secretion. Growth of hard tissues like bone occurs through both endochondral ossification and intramembranous ossification. Endochondral ossification involves cartilage models that are later replaced by bone, while intramembranous ossification forms bone directly from mesenchymal condensations. The skull, jaw, and face develop through both processes during embryogenesis and postnatal growth.