Since this slide has only one side of the cervix-vagina, mirror images were placed together for orientation. The arrow indicates the cervical opening (called the os) leading into the cervical canal. It is at this point that the mucus-secreting simple columnar epithelium of the cervical canal is replaced by a stratified squamous, nonkeratinized epithelium covering the vaginal portion of the cervix (*) and vagina (V). Invaginations of the lining of the cervical canal represent the cervical glands (Gld). Clogging of the openings of these glands cause the appearance of cysts (Cy).