The process of bone growth is influenced by two main and complementary factors: first, the regulation of longitudinal growth by the metaphyseal cartilage, and second, the shaping of bone by the periosteum. These two factors are synchronized in their action, in that the new bone created at the metaphyseal cartilage is molded into its predestined shape by periosteal osteoclastic and osteoblastic activity. This synchronized action was designated by Hunter “modeling of the bone.” The new bone is formed with a waist-like “constriction” above the metaphysis and not as a direct continuation of the old bone. The “double contour” seen in roentgenograms of the long bones of infants in the first months of life, regarded by Glaser as the “effect of crests of bone,” is in my opinion to be attributed to periosteal activity, in the sense of normal modeling. This modeling process, which conserves the tubular form at the metaphysis, can be observed by superimposing roentgenograms of a limb of an infant obtained at differe...