According to the Encyclopedia Britannica, the cervix is approximately 1.6 inches long and projects less than 1 inch into the upper vaginal cavity. It is lowest region of the uterus. The cervix attaches the uterus to the vagina and provides a passage between the vaginal cavity and the uterine cavity.
The Encyclopedia Britannica states that the cervical opening into the vagina is called the external os. The endocervical canal is the cavity that runs the length of the cervix. The opening of the endocervical canal into the uterine cavity is called the internal os. The endocervical canal transports sperm into the uterine cavity, allows blood to escape from the uterus during menstruation and supplies mucus, which is a thick lubricating protein, to the female reproductive tract. The canal expands during childbirth.