This series models consists of six development phases and each parts shows a state of prenatal cervix and birth canal. The whole models demonstrate the relations between the scope of the expanding of the orifice of cervix, and the range of cervical tunnels, as well as the relation between the position of the head of fetus and the square of ischial spine.

•    Stage 1 - no dilation of cervix; cervical canal does not disappears ; the position relation between fetal head and ischial spine place is -5

•    Stage 2 - 2 cm cervical dilation ; disappears 50% of cervical canal ; the position relation between fetal head & ischial spine place is - 4;

•    Stage 3 - 4 cm cervical dilation ; cervical canal completely disappears; the position relation between fetal head & ischial spine place is - 3;

•    Stage 4 - 5 cm cervical dilation ; cervical canal completely disappears; the position relation between fetal head & ischial spine place is - 0;

•    Stage 5 - 7 cm cervical dilation ; cervical canal completely disappears; the position relation between fetal head & ischial spine place is +2;

•    Stage 6 - 10 cm cervical dilation ; cervical canal completely disappears; the position relation between fetal head & ischial spine place is +5;