What is the cervix?

The cervix is the lower third portion of the uterus which forms the neck of the uterus that opens into the vagina. The narrow opening of the cervix is called the os. The os allows menstrual blood to flow out, and widens during labor to allow the passage of the fetus through the vagina during childbirth.

The cervix is covered by the epithelium which is made of a thin layer of cells. The cells of the epithium are either squamous or columnar. Squamous cells are flat and scaly, while columnar cells appear column-like.

Image of Normal Cervix- From Female Genital Pathology.

Pap Smears- From your About.com Guide.