Anomalous hip joints of a twenty-six-week male fetus were studied by histological and roentgenographic techniques: the femoral heads were normal and both acetabula were abnormal, the cause of which could be genetic. The extent to which the roof of the acetabulum ossified in the presence of marked changes in the joint is significant. Neither the absence of the femoral head from its normal site nor its presence in an abnormal site affected primary ossification. Therefore, the changes in ossification of the acetabular roof of young animals after experimental hip dislocation should be interpreted with caution until more is known about the normal and anomalous development of the hip joint in man.