The lower part of the female reproductive tract (see REPRODUCTIVE SYSTEM) through which a baby is delivered. It is a muscular passage leading from the labial entrance to the UTERUS. It is lined with mucous membrane and receives the erect PENIS during sexual intercourse. The semen is ejaculated into the upper part of the vagina; from there the sperms must pass through the cervix and uterus to fertilise the ovum in the Fallopian tube.