Growing bone. Light micrograph of the growing end of a long bone. The head (epiphysis) of the bone (right) is covered with articular cartilage (bright blue), which protects the bone from wear and tear where it articulates with another bone. Behind the cartilage is an area of spongy bone consisting of trabeculae filled with bone marrow (purple). Bone growth occurs in the epiphyseal plate, which is made of hyaline cartilage (dark blue). Here, cartilage cells (chondrocytes) divide, enlarge and eventually die. The cartilage matrix is replaced with bone, thus lengthening the shaft (diaphysis, left) of the bone. Magnification: x20 when printed 10cm wide.