[Multiplication of the different varieties of cells of the mouse pubic symphysis during growth and early gestation: radioautographic study with the use of tritiated thymidine].

1. A radioautographic study was undertaken after injection of tritiated thymidine during post-natal growth. The mitotic activity was localized in the three constituents of the mouse pubic symphysis: - in the osteogenic cartilage, labelled nuclei are numerous throughout animal growth; - in the articular cartilage, labelled nuclei are seldom encountered; - in the medial region, the chondroblasts, elongated dorso-ventrally, and the fibroblasts of the dorsal ligament show numerous labelled nuclei. 2. During the first pregnancy, the mitotic activity of the three constituents were examined separately: - in the osteogenic cartilage, the number of labelled cells increases at the beginning of the first pregnancy : the tibia epiphyseal cartilage apparently simultaneously shows revival of mitotic activity. After the 15th day of pregnancy, the osteogenic cartilage disappears by endochondral ossification; - in the articular cartilage and fibrocartilage, no mitotic activity is detectable as long as their typical characteristics are conserved. However, mititic activity becomes evident again when these cartilaginous cells cease to be surrounded by the typical chondroid matrix and become incorporated into the ligament. Cell multiplication therefore participated in symphyseal ligament dilatation.