This image typifies bone growth that occurs along a metaphysis ossification center of a long bone cut in longitudinal section. Note the formation of a marrow cavity (diaphyseal marrow cavity) which enlarges as it expands into the epiphyseal cartilage. During this process, a cartilaginous model of the bone is transformed through a dynamic process into the "adult" bone. It is important to note, that the formation of bone by endochondral bone formation, is NOT the result of calcification of cartilage. Intramembranous bone formation, by contrast, is the development of bone from condensation of mesenchymal cells in the region of the bone to be formed. In this situation, the aggregated mesenchymal cells differentiate into osteoblasts, which then form the bone matrix as non-calcified bone, called osteoid. The osteoid is subsequently calcified.