Bag of membrane ruptures:
Membranes usually rupture after full dilatation of cervix or sometimes even beyond, in the second stage.
Early Rupture of Membranes:

Rupture of membranes any time after the onset of labour but before full dilatation of cervix.

Premature Rupture of Membrane:

Rupture of membranes before the onset of labour.
Sometimes the membranes remain intact until completion of delivery, the fetus is then born surrounded by them and the portion covering the head of the newborn infant is known as the Caul.
Before full dilatation of cervix
After full dilatation of cervix
After head is engaged
With excessive show