Cervix
The cervix is the bottom part of the womb (uterus) of the female reproductive system. The cervix is about 1 inch long. It is in the shape of a cylinder. The shape changes during pregnancy. There is a thin, central cervical canal that runs through its length. This canal connects the womb and the vagina. The opening into the uterus is called the internal os. The opening into the vagina is called the external os. The lower part of the cervix bulges into the top of the vagina. The cervix has been written about since at least the time of Hippocrates, over 2,000 years ago.