The influence of pressure upon the fetal head during labour.

In contracted pelvis, moulding of the skull bones is caused by the force of the amniotic fluid pressure and the resistance of the pelvis. In normal labour and abnormal uterine action the moulding of the skull bones is caused by the head to cervix pressure, as has been demonstrated by intra-uterine tokometry. By contrast, in the contracted pelvis there are no mouldings between the two parietal bones. In breech presentation during the first stage of labour the moulding of the skull bones is explained, by the differing resistance of the various skull bones against the amniotic fluid pressure.