variation. It is of a circular shape, and the cord is usually inserted

Fig. 148.

into its centre. It may be attached to any part of the uterus, but is usually found towards the fundus. Of its two surfaces, that which corresponds to the uterus, is divided into irregularly rounded lobes or cotyledons, and it is covered by a soft and delicate cellulo-vascular membrane, which, according to CHAUSSIER,who believes that the decidua invests the whole ovum, is the decidua. Wrisberg, Lobstein, and Desormeaux, how

ever, who consider that the decidua disappears from behind the

Fig. 149.

placenta about the fourth or fifth month, regard it as a new membrane; whilst Velpeau maintains that the decidua never exists there.

The foetal or umbilical surface is smooth, polished, covered by the chorion and amnion and exhibits the distribution of the umbilical vessels, and the mode in which the cord is attached to the organ.

The following are the anatomical constituents of the placenta, as described by anatomists. First. Bloodvessels, from two sources,the mother and the foetus. The former proceed from the uterus, and consist of arteries and veins, of small size but considerable number. The vessels, which proceed from the foetus, are those that constitute the umbilical cord;—viz. the umbilical vein, and the umbilical arteries. These vessels, after having penetrated the foetal surface of the placenta, divide in the substance of the organ, so that each lobe has an arterial and a venous branch, which ramify in it, but do not anastomose with the vessels of other lobes. Secondly. Expansions of the chorion, which are described by some as dividing into cellular sheaths and accompanying the vessels to their

final ramifications;—an arrangement which is, however, contested by others. Thirdly. White filaments, which are numerous in proportion to the advancement of pregnancy, and which seem to be only obliterated vessels. Fourthly. A kind of intermediate cellular tissue, serving to unite the vessels together, and which has been regarded, by some anatomists, as an extension of the decidua accompanying those vessels. Lastly. A quantity of blood poured into this intermediate cellular tissue, which may be removed by washing.

In addition to these constituents, a glandular structure has been presumed to exist in it; as well as lymphatic vessels; and Chaussier and Ribes say nerves, proceeding from the great sympathetic of the fœtus.

The uterine and the foetal portions of the placenta are quite distinct from each other, during the two first months of foetal life; but afterwards they constitute one mass. Still the uterine vessels remain quite distinct from the foetal; the uterine arteries and veins communicating freely with each other, as well as the foetal arteries and veins; but no direct communication existing between the maternal and fœtal vessels.

4. Umbilical cord.—From the foetal surface of the placenta a cord of vessels passes, which enters the umbilicus of the foetus, and has hence received the name umbilical cord, as well as that of navel-string. It forms the medium of communication between the fœtus and the placenta.

During the first month of fœtal existence, the cord is not perceptible; the embryo appearing to be in contact, by the anterior part of its body, with the membranes of the ovum.

Fig. 150.

In an embryo, a month old, Beclard observed vessels creeping for a certain space between the membranes of the ovum, from the abdomen of the foetus to a part of the chorion, where the rudiments of the future placenta were visible. During the fifth week, the cord can first be detected, at which period it is straight, short, and very large, owing to its containing a portion of the intestinal canal. It presents also, three or four dilatations, separated by as many contracted portions or necks; but these gradually disappear, the cord lengthens and be

comes smaller, and

occasionally it is twisted, knotted and tuberculated in a strangely in

explicable manner, (Fig. 150.) At the full period, the length of the cord varies; but, on the average, it is perhaps about twenty inches. It is composed of three vessels,—the umbilical vein, two arteries of the same name, of a peculiar jelly-like substance, and is surrounded, as we have seen, by the amnion and chorion. The vessels will be more particularly described hereafter. They are united by a cellular tissue, containing the jelly of the cord, a thick albuminous secretion, which bears some resemblance to jelly, and the quantity of which is very variable. In the foetus, the cellular tissue is continuous with the sub-peritoneal cellular tissue; and in the placenta, it is considered to accompany the ramifications of the vessels.

It has been already remarked, that Chaussier and Ribes have traced branches of the great sympathetic of the fœtus as far as the placenta.

According to most obstetrical physiologists, when pregnancy is multiple, the ova in the uterus are generally distinct, but contiguous to each other. By others, it has been affirmed that two or more children may be contained in the same ovum, but this appears to require confirmation. The placenta of each child, in such multiple cases, may be distinct; or the different placentæ may be united into one, having intimate vascular communications with each other. At other times, in twin cases, but one placenta exists. This gives origin to two cords, and at others, to one only, which afterwards bifurcates and proceeds to both fœtuses. Maygrier, however, affirms unconditionally, that there is always a placenta for each foetus; but that it is not uncommon, in double pregnancies, to find the two placentæ united at their margins; the circulation, however, of each foetus being distinct, although the vessels may anastomose.

II. OF THE FŒTUS.—The ovule does not reach the uterus until towards the termination of a week after conception. On the seventh

old.

Fig. 151.

or eight day it has the appearance referred to in the case so often cited from Sir EVERARD HOME; the future situations of the brain and spinal marrow being recognisable with the aid of a powerful, microscope. On the thirteenth or fourteenth day, according to Maygrier, the ovum is perceptible in the uterus, and of about the size of a pea, containing a turbid fluid, in the midst of which an opaque point is suspended,—the punctum saliens. Ovum and embryo, fifteen days The weight of this has been valued at about a grain.

On the twenty-first day, the embryo appears under the shape of a large ant, according to Aristotle; of a grain of lettuce; of a grain of barley, according to Burton; or of the malleus of the ear, according to Baudelocque. At this period, the different

parts of the embryo have a little more consistence; and those that have afterwards to form bone, assume the cartilaginous condition. On the thirtieth day, some feeble signs of the principal organs and of the situation of the upper limbs are visible;—length four or five lines.

Appearance of ovum and embryo, twenty-one days old.

About the forty-fifth day, the shape of the child is determinate; and it now, in the language of some anatomists, ceases to be the embryo, and becomes the foetus.

Fig. 152.

The limbs resemble tubercles, or the shoots of vegetables; the body lengthens, but preserves its oval shape, the head bearing a considerable proportion to the rest of the body. The base of the trunk is pointed and elongated. Blackish points, or lines, indicate the presence of the eyes, mouth, and nose; and similar, parallel points correspond to the situation of the vertebræ. Length ten lines.

In the second month, most of the parts of the foetus exist. The black points, which represented the eyes, Appearance of the enlarge in every dimension; the eyelids are sketch-foetus at forty-five days. ed, and are extremely transparent: the nose begins to stand out; the mouth increases, and becomes open; the brain is soft and pulpy; the heart is largely developed, and opaque lines set out from it; which are the first traces of large vessels. The fingers and toes are distinct.

Fig. 153.

In the third month, the eyelids are more developed, and firmly closed. A small hole is perceptible in the pavilion of the ear. The alæ nasi are distinguishable. The lips are very distinct, and approximated, so that the mouth is closed. The genital organs of both sexes un- at two months. dergo an extraordinary increase during this month. The penis is VOL. II.

45

Appearance of the foetus

very long; the scrotum empty, frequently containing a little water. The vulva is very apparent, and the clitoris prominent. The brain, although still pulpy, is considerably developed, as well as the spinal marrow. The heart beats forcibly. The lungs are insignificant; the liver very large, but soft and pulpy, and appears to secrete scarcely any bile. The upper and lower limbs are developed. Weight two and a half ounces: length three and a half inches.

Appearance of the foetus at three months, in its membranes.

During the fourth month, all the parts acquire great development and character, except perhaps the head and the liver, which increase less in proportion than the other parts. The brain and spinal marrow acquire greater consistence; the muscular system, which began to be observable in the preceding month, is now distinct; and slight, almost imperceptible movements begin to manifest themselves. The length of the foetus is, at the end of one hundred and twenty days, five or six inches; the weight four or five

ounces.

During the fifth month, the development of every part goes on; but a distinction is manifest amongst them. The muscular system is well-marked, and the movements of the fœtus unequivocal. The head is still very large, compared with the rest of the body, and is covered with small, silvery hairs. The eyelids are glued together. Length seven to nine inches; weight six or eight ounces. If the