Remember, the wall of the uterus not only has that endometrium, but it also contains smooth muscle. And that smooth muscle is capable of contracting. And so in the first stage of the birthing process, also known as labor, this is when the contraction of that uterus begins. And as a result of these contractions, that fetus, the head of the fetus, begins to position and begins to move towards the cervix. So remember, the cervix is that section between the uterus and the tract of the vagina. What also happens is the cervix is normally very rigid.