The long endochondral bones keep on growing in length after birth until optimum length of the bone has been achieved during the adulthood. The growth in length takes place by the continuous proliferation of the cartilage cells in the juxtaepiphysial region of the growth plates. The epiphysial cartilages continue to develop new cartilage cells as long as the bone continues to grow in length. Finally, when the adult length has been achieved, the cartilage cells in the epiphysial cartilages cease to proliferate and this cartilage also becomes ossified. Thus the bone shaft (diaphysis) becomes finally united tothe epiphysis. In the adult bone a faint bony ridge, called epiphysial line, marks this union at each end of the long bone.