The young of some of the lower animals are observed to perform certain peculiar motions, during delivery, by which it is much facilitated; and this is considered a proof, by some, that voluntary movements of the fœtus assist in the process. Certainly if it be supposed, as we have shown there is good grounds for doing, that the child assists in placing itself in the best _position_, it is equally probable that it also assists in its own expulsion, in other ways. SIGNS OF DELIVERY. _Premonitory Signs._--A few days before delivery the Uterus descends much lower, so that the diaphragm and stomach are less pressed upon, and the breathing and digestion becomes easier in consequence. The ease which is thus experienced is sometimes so great that the female becomes unusually animated and cheerful, and cannot think she is so near her travail. This is not always the case however, for some on the contrary feel very uncomfortable and melancholy. The lips of the Vulva are also apt to swell and become painful, and the lower limbs numbed and cramped, owing to the child's head pressing on the large nerves. The neck of the bladder is also very liable to be compressed, so that a constant desire is felt to urinate, and a similar trouble may also be experienced in the Rectum. Most of these inconveniences, but particularly the numbness and cramps in the limbs, are not likely to be experienced except when the head presents, because no other part is so formed as to be able to descend sufficiently low; when they are felt therefore, the female may console herself by the reflection that they indicate, with tolerable certainty, that the child is presenting in the best position it can for a safe and speedy delivery. Standing, or walking, usually become more difficult, and swelling of the external parts, or piles, are apt to occur. With some females also, a sudden diarrhœa, or vomiting, takes place, and troubles them up to the period when labor commences. Finally the Uterus begins to contract, though insensibly at first; the Abdomen becomes unusually hard, and flying pains are experienced, particularly with first children. This continues with more or less of intermission, up to the actual period of labor, which is usually divided into _three_ periods, each of which must be considered separately. CHAPTER XVI. THE PROGRESS, PHENOMENA, AND DURATION OF NATURAL LABOR. FIRST PERIOD.