Cambium cellularity (A), maximum cambium thickness (B) and cambium cell density (C) of periosteum from 12-month old rabbit tibia measured 1, 3, 5, or 7 days post injection of vehicle, TGF-β1 (20, or 200 ng), or TGF-β1 (200 ng) plus IGF-1 (2 μg). Lowercase letters indicate the results of post-hoc testing using least squares means differences Student’s t-test (p<0.05). Columns with letters in common are not statistically different from one another.