[Mechanical action of obstetrical forceps on the fetal skull].

By means of schematic illustrations we demonstrate the working point of the power of labour, obstetrical forceps and vacuum extractor, The bones of the fetal skull are by sutures movable fastened together. Every extraction so will rise the intracranial pressure of the fetus, because the resistance of the birth canal tissues must be overcome. This for the extraction needed power and rising of the intracranial pressure is independent from the instrument with which the extraction is carried out. It is impossible to make a "cage" around the fetal head with the Shute forceps during extraction, to protect the fetal head from the extraction power. Another question is, that some instruments (included vacuum extractor) can limit the used power. By using forcipes with crossed lock without fixation the forces for extraction are not limited and there is a need of better operative technic. By the comparison of the forcipes from Shute, Naegele and Zweifel we can summarize, that for success is decided the indication and good operative technic and not the instrument. Every instrument for vaginal extraction has advantages and disadvantages in different obstetrical situations.