Illustration of a section through a female pelvis showing the uterus (womb) in early labour, or childbirth. The front of the body is at right, with the spine at left. The fluid-filled amniotic sac that has cushioned the foetus during pregnancy is being pushed into the opening of the birth canal (vagina). The pressure will cause it to rupture and leak from the vagina, which is known as the waters breaking. From An Improved System of Midwifery, by Wooster Beach (1794-1868), published in 1851.