The ossification status of Wistar rat fetuses at the end of gestation.

We present a comprehensive description of spontaneous skeletal development of Wistar rat fetuses close to parturition. Fetuses were collected on the day of expected parturition and one and two days before (Gestation Days 21-23) and skeletal development state was examined. Data is presented on an individual fetal basis to allow insights in developmental patterns. The distal parts of the limbs and the cervical and caudal vertebral column were identified as areas of the greatest developmental difference in the examined time frame. Extensive knowledge of the ossification process in individual fetuses allows a better resolution of deviations from normal and gives valuable information for the grading of delayed maturation and structural deviations. The data base is helpful to overcome the bottleneck of coincident occurrence of low incidences of skeletal abnormalities in the dose groups and the control group complicating risk assessment of test articles.