Since very early in pregnancy, you will remember, your uterus has been growing alternately hard and soft as the muscles have contracted and relaxed. But these contractions have been as painless, and so far as we know, as fruitless as the contractions of a boy’s biceps as he clenches his fist and produces a hard lump on his arm. But when the baby is ready to take up his life among the rest of us human beings, the contractions of your uterine muscles are altered in such a manner that you gradually become conscious of them and they become so purposeful that they are able slowly but steadily to force the baby down through that narrow part of the pelvis called the inlet, through the cervix, and finally out into the world. Since, at the proper time you will be able to help these altered muscular contractions to accomplish their high purpose, you will want to watch their progress, with your mind’s eye, as far as possible. Recall, for a moment, the fact that the baby is contained in a sac of fluid in the cavity of the uterus, above the cervix; that the cervix, below, is a canal drawn in tightly at the upper end, or internal os, and also at the lower end, or external os. Quite evidently after the baby’s head has been squeezed through the pelvic inlet by pressure of the uterine contractions, the cervix must open widely in order that he may pass through it, too. And so Nature gradually stretches this narrow canal by using the lowermost part of the bag of waters as a water-wedge and forcing it down into the internal os, a little farther with each pain. The opening grows wider and wider as the bag of waters is pressed farther and farther down into the cervical canal, which also widens slowly, and finally the external os, too, is stretched wide open by the water-wedge. Fig. 22 shows how the cervix looks with the bag of waters pressed against the upper opening and how the entire canal is gradually dilated by this wedge, as it is pressed downward. As you doubtless know, the process of your baby’s emergence into the world and separation from your body is termed =labor=. The onset of labor is usually marked by the expectant mother becoming conscious of the uterine contractions through dragging pains which are felt first in the small of the back and then in the lower part of the abdomen and thighs. In the beginning the pains are feeble and infrequent, but they gradually grow more severe and more frequent. Sometimes the first sign of labor is a gush of fluid, caused by the rupture of the membranes, or the appearance of blood, but these are not typical. Intestinal colic is sometimes mistaken for labor pains by women who are pregnant for the first time, but when the cramps come regularly and the uterus is felt, through the abdominal wall, to grow hard as the pain increases, and soft as it subsides, there can be no doubt that they are labor pains.