CHAPTER IX.
THE APPENDAGES OF THE FŒTUS AT TERM.
THE MEMBRANES.
The uses and arrangements of the membranes surrounding the Fœtus have already been explained, so that little more is needed to be said here, because they are not much different at the full term from what they are at an earlier period, excepting perhaps that the amnion is a little more dense and firm. This membrane appears not only to surround the Fœtus like a bag, to contain the waters, but is also reflected close on to its body, like its skin, with which in fact it is thought by some to be connected. The child is certainly born with this membrane still on its body, and does not part with it till some days after birth, when it peels off like a thin dead skin, or powder.
The waters, enclosed within the Amnion, (see Plate XII,) have now increased to their greatest quantity; and there is also, in most cases, a second body of fluid between the Amnion and the Chorion, which coming away before the real discharge, is called the false waters.—(See Plate XII.)
The quantity of the true waters, at birth, is about twenty, or from that to thirty ounces, but is very variable. It is of a greenish color, rather muddy, and heavier than water. It contains albumen, (white of egg,) sulphate of soda, and lime. Ninety-eight per cent. of it however, is pure water. It appears to be excreted, like perspiration, from the surface of the membranes, and most likely is merely the watery portion of the blood exuded through. The uses of this fluid are various. As already stated, it probably supplies some nutriment to the fœtus, which it also protects, in a great measure, from pressure and from concussions. It also prevents the limbs from adhering, and helps to distend the mouth of the Womb, in the earlier stages of labor, besides affording an abundant slippery fluid for the purpose of lubricating the passages, thus making the passage of the child more easy.—(See Plate XII.)
The other two membranes, the Chorion and Decidua, are not of much importance in our present explanation; and practically, in fact, the whole three may be regarded as one envelope, surrounding the child and the waters in which it floats.
THE PLACENTA.
At the full term the Placenta, (See Plate XII,) is about six or seven inches in diameter, and nearly circular, though often irregular. Its thickness varies from one to two inches, and is greatest where the cord is inserted. Sometimes it is very large, or very thick, and may then be difficult to extract, and even cause serious accidents.
As already explained the Placenta is composed of a mass of blood-vessels, by means of which the blood of the fœtus is, in some way, brought into contact, or commingled with that of the mother. Its uterine face is irregular, being broken into lobes, or cotyledons, on which may be seen a vast number of little veins and arteries, corresponding with others on the inner surface of the Womb. Its outer surface is of a grey red color, and covered with the fœtal membranes, under which the large blood-vessels can be traced. The Placenta is usually attached to one side of the Uterus, near the fundus, or at the fundus, but sometimes it grows wholly, or in part, over the mouth of the Womb; an occurrence which may cause serious consequences.
When there is more than one child each usually has a separate placenta, and they are all intimately connected. In some rare cases however, one placenta only exists with twins. Each child has also a separate amnion, and waters; but there may be only one chorion and decidua for the whole, or each may have a complete set of membranes itself. Instances have been known however, of two children being enclosed in the same amnion, and surrounded by the same waters, having but one placenta between them.
These possible diversities show the accoucheur how necessary it is for him, in any case of multiple pregnancy, to be sure that he has abstracted all the after birth; and they also caution him not to proceed to unnecessary manipulations merely because it is not the same as in other cases.
THE UMBILICAL CORD.
This is composed, as already stated, of an artery and two veins, which twist round the artery, like the strands of a rope. These are all enclosed in a sheath, and surrounded by a thick kind of mucus, called the Gelatine of Wharton. Its thickness is about that of the little finger, though it may be much larger, having been seen as thick as the child's body. Its usual length is about eighteen or twenty inches, but it has measured as much as five feet. Then again it has been found so small that the vessels in it could not nourish the child. These exceptional variations however, are very rare. The veins may also be enlarged, or full of knots, and the circulation may be so much impeded thereby as to cause abortion. The various accidents which may result from anomalies in the cord will however, engage our attention in another place.
SECTION IV.
THE MECHANISM OF DELIVERY IN ALL THE DIFFERENT PRESENTATIONS AND POSITIONS OF THE FŒTUS.