The cervical canal varies greatly in length and width between women or over the course of a woman's life, and it can measure 8 mm (0.3 inch) at its widest diameter in premenopausal adults. It is wider in the middle and narrower at each end. The anterior and posterior walls of the canal each have a vertical fold, from which ridges run diagonally upwards and laterally. These are known as "palmate folds", due to their resemblance to a palm leaf. The anterior and posterior ridges are arranged in such a way that they interlock with each other and close the canal. They are often effaced after pregnancy.