Abstract
Serial contact auto-radiographs were prepared from the dried skulls of rats (birth to 62 days) killed at variable intervals after intraperitoneal injection of radioactive calcium (Ca45). Growth by surface deposition on facial aspects and the contribution by cartilage replacement in the cranial base and nasal septum to the increase in length of the face is shown by heavy deposition of Ca45 in these regions. The pattern of Ca45 uptake around the molar roots suggests their outward migration as jaw width increases.