It often happens that the foetus quits the matrix without bursting the membranes, and consequently without the contained liquor flowing out. This kind of delivery appears to be most natural, and resembles that of most animals; nevertheless, the human foetus commonly pierces its membranes by the resistance it meets with at the orifice of the matrix. It also sometimes brings away part of the amnios, and even the chorion, upon its head like a cap. When these membranes are pierced or torn, the liquors, called the _waters_, which they contain flow out, and the sides of the orifice of the matrix, and the vagina, being thus moistened, give way more easily to the passage of the child. After the flowing of this liquor there remains sufficient room in the matrix for the midwife to return the child, if the position is unfavourable. When the foetus is come out the delivery is not entirely completed, the placenta and membranes remain in the matrix, and the new-born infant adheres to them by the umbilical cord; the hand of the midwife, or the weight of the body of the infant alone, draws them out by means of this cord. Those organs which were necessary to the life of the foetus become useless, and even noxious to the new-born infant. They are instantly separated from the body of the child, by tying the umbilical cord about an inch distance from the navel, and by cutting it about an inch from the ligature. The remainder of this cord dries away, and separates of itself from the navel, about the sixth or seventh day. On examining the foetus previous to its birth we may form some idea of its natural functions. It has organs, which are necessary to it while in the womb of its mother, but which become useless. For the better understanding the mechanism of these functions, we must explain a little more particularly the nature of those necessary parts, the umbilical cord, the membranes, the liquor which they contain and the placenta. The umbilical cord, which is attached to the body of the foetus at the navel, is composed of two arteries and one vein; these prolong the circulation of the blood, but the vein is larger than the arteries. At the extremity of the cord each of these vessels divide into an infinity of ramifications, which extend between two membranes. They separate at equal distances from the common trunk; so that these ramifications are round and flat, and are called, when thus collected, the _placenta_. The external surface, which is applied against the matrix, is convex; the internal concave. The blood of the foetus circulates in the cord, and in the placenta. The arteries of the cord spring from two large arteries of the foetus, and carry the blood through the arterial ramifications of the placenta; from thence it passes into the venous branches which carry it into the umbilical vessels; these communicate with a vein of the foetus, in which vessels it is received.