The cervix (from Latin "neck") is the neck of the uterus. This is the place where the uterus joins with the top end of the vagina. It is normally blocked by a muscosal plug which helps to prevent infection, and which has to evacuated before the birth process can begin.
In humans it is associated with a particular form of cancer which is detectable by cytological study of epidermal cells remove from the cervix in a process known as the pap smear.