Bone growth. Light micrograph of a section through a growing long bone. The head of the bone (at top) is covered in articular cartilage (blue), which protects it from wear and tear as it articulates with other bones. Behind the head is an area of spongy bone consisting of trabeculae filled with bone marrow (dark purple). Bone growth occurs in the epiphyseal plate, which is made of hyaline cartilage (blue band across bottom). Here cartilage cells (chondrocytes) divide, enlarge and eventually die. The cartilage matrix is replaced with bone formed from osteoblast cells. This process is known as ossification and serves to increase the length of the bone shaft (diaphysis).