Figure 1.

Two major modes of the ossification that constructs the human skeleton. Clavicle and cranial bones are formed through intramembranous ossification, where osteoblasts create the prototype (left) and grow the bone (shown in pink). Most of the other bones are initially formed by chondrocytes as cartilage anlagen (left, shown in light blue), and chondrocytes grow them at the growth plate inside and develop articular cartilage at the epiphysis. Along with bone growth, ECM is mineralized by osteoblasts. In the growth plate, chondrocytes follow a serial differentiation process from resting (R), proliferation (P), mature (M), and hypertrophic (H) stages towards ossification (bottom).