The cervix (from Latin "neck") is the lower, narrow portion of the uterus
where it joins with the top end of the vagina. It is cylindrical or conical
in shape and protrudes through the upper anterior vaginal wall.
Approximately half its length is visible with appropriate medical equipment;
the remainder lies above the vagina beyond view. It is occasionally called
"cervix uteri", or "neck of the uterus".
The portion projecting into the vagina is referred to as the portio
vaginalis or ectocervix. On average, the ectocervix is 3 cm long and 2.5 cm
wide. It has a convex, elliptical surface and is divided into anterior and
The ectocervix's opening is called the external os. The size and shape of
the external os and the ectocervix varies widely with age, hormonal state,
and whether the woman has had a vaginal birth. In women who have not had a
vaginal birth the external os appears as a small, circular opening. In women
who have had a vaginal birth, the ectocervix appears bulkier and the
external os appears wider, more slit-like and gaping.
The passageway between the external os and the uterine cavity is referred to
as the endocervical canal. It varies widely in length and width, along with
the cervix overall. Flattened anterior to posterior, the endocervical canal
measures 7 to 8 mm at its widest in reproductive-aged women.
The endocervical canal terminates at the internal os which is the opening of
the cervix inside the uterine cavity.