_Dilatation of the perineum._ As pain succeeds pain, gradually increasing both in force as well as duration, the head descends along the vagina, and begins to press against the perineum; the rectum becomes flattened; the sphincter ani dilated, and therefore any fæcal matter which may have been lodging there is unavoidably expelled; the anterior wall of the rectum is pressed close against the anus, and where the pressure is very great, even protrudes somewhat through it; the hæmorrhoidal veins are frequently much distended, and form a roll of cushiony swelling around the anus. A small quantity of liquor amnii dribbles away from time to time, but is neither during a pain, nor during the absence of a pain, for in the former case the pressure of the head acts as a plug and prevents its escape, and in the latter there is no uterine contraction present to expel it: the liquor amnii dribbles away only at the moment when a pain is coming on or going off. _Expulsion of the child._ As the head descends farther it begins to press more powerfully on the perineum, and during each pain pushes it out like a large ball; and then, as a contraction goes off, and the resiliency of the soft parts regain their superiority, it retires again. The breadth of the perineum (viz. from the anus to the vulva) increases, whilst it diminishes considerably in thickness, especially towards its anterior margin. Whilst passing through the inferior aperture or outlet of the pelvis, the head advances more or less forwards under the pubic arch, and begins to distend the os externum; during a pain it separates the labia, and protrudes between them, and again retires as the pain goes off; a larger and larger portion of the head gradually forces itself through the os externum as this dilates; the perineum becomes still thinner, so that at length it is scarcely thicker than parchment. When more of the head has passed through, it does not now recede when the pain goes off; the os externum and perineum are at their greatest distension, for the largest diameter of the head, which is presented to the os externum is now encircled by it; the next pain brings the head into the world.