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forms a sheath to each of the chorion villi, which it separates from the maternal blood. This new glandular structure he describes as secreting a fluid, termed the "uterine milk," which is absorbed by the villi of the chorion, just as the mother's milk is absorbed by the villi of the intestines, and it is with this fluid alone that the chorion villi are in direct contact. The sheath thus formed to each villus is doubtless analogous to the layer of cells which Goodsir described as encasing each villus, but is attributed to a new structure formed after conception.

The existence of the maternal sinus system in the placenta is altogether denied by anatomists of eminence whose views are worthy of careful consideration. Prominent amongst these is Braxton Hicks,' who has written an elaborate paper on the subject. He holds that there is no evidence to prove that the maternal blood is poured out into a cavity in which the chorion villi float, and he believes that the curling arteries, instead of entering the so-called maternal portion of the placenta, terminate in the decidua serotina. The hypertrophied chorion villi at the site of the placenta are firmly attached to the decidual surface, into which their tips are imbedded. The line of junction between the decidua reflexa and serotina forms a circumferential margin to, and limits, the placenta. The arrangement of the foetal portion of the placenta on this view is very similar to that generally described, but the villi are not surrounded by maternal blood at all, and nothing exists between them, unless it be a small quantity of serous fluid. The change in the foetal blood is effected by endosmosis, and Hicks suggests that the follicles of the decidua may secrete a fluid, which is poured into the intervillous spaces for absorption by the villi.

Functions of the Placenta.-It will thus be seen that anatomists of repute are still undecided as to important points in the minute anatomy of the placenta, which further investigation will doubtless clear up. The main functions of the organ are, however, sufficiently clear. During the entire period of its existence it fills the important office of both stomach and lungs to the foetus. Whatever view of the arrangement of the maternal blood vessels be taken, it is certain that the foetal blood is propelled by the pulsations of the foetal heart into the numberless villi of the chorion, where it is brought into very intimate relation with the mother's blood, gives off its carbonic acid, absorbs oxygen, and passes back to the foetus, through the umbilical vein, in a fit state for circulation. The mode of respiration, therefore, in the foetus is analogous to that in fishes, the chorion villi representing the gills, the maternal blood the water in which they float. Nutrition is also effected in the organ, and, by absorption through the chorion villi, the pabulum for the nourishment of the foetus is taken up. It also probably serves as an emunctory for the products of excretion in the foetus. Picard found that the blood in the placenta contained an appreciably larger quantity of urea than that in other parts of the body, this urea probably being derived from the fœtus.

Obst. Trans., 1873, vol. xiv. p. 149.

Claude Bernard also attributed to it a glycogenic function,' supposing it to take the place of the foetal liver until that organ was sufficiently developed.

Finally, we find that the temporary character of the placenta is indicated by certain degenerative changes, which take place in it previous to expulsion. These consist chiefly in the deposit of calcareous patches on its uterine surface, and in fatty degeneration of the villi and of the decidual layer between the placenta and the uterus. If this degeneration be carried to excess, as is not unfrequently the case, the foetus may perish from want of a sufficient number of healthy villi through which its respiration and nutrition may be effected.

The umbilical cord is the channel of communication between the foetus and placenta, being attached to the former at the umbilicus, to the latter generally near its centre, but sometimes, as in the battledore placenta, at its edge. It varies much in length, measuring on an average from eighteen to twenty-four inches, but in exceptional cases being found as long as fifty or sixty, and as short as five or six inches.

When fully formed it consists of an external membranous layer formed of the amnion, two umbilical arteries, one umbilical vein, and a considerable quantity of a transparent gelatinous substance surrounding the vessels, called Wharton's jelly, which is contained in a fine network of fibres, and is formed from the somato-pleural layer of the mesoblast in the cord. At an early period of pregnancy, in addition to these structures, the cord contains the pedicle of the umbilical vesicle, with the omphalo-mesenteric vessels ramifying on it, and two umbilical veins, one of which soon atrophies and disappears. No nerves or lymphatics have been satisfactorily demonstrated in the cord, although such have been described as existing. The vessels of the cord are at first straight in their course, but shortly they become greatly twisted, the arteries being external to the vein, and in nine cases out of ten the twist is from left to right. Various explanations have been given of this peculiarity, none of them entirely satisfactory. Tyler Smith attributed it to the movements of the foetus twisting the cord, its attachment to the placenta being a fixed point; this would not, however, account for the frequency with which the spiral turns occur in one direction. Mr. John Simpson attributed it to the greater pressure of the blood through the right hypogastric artery, on account of that vessel having a more direct relation to the aorta than the left. The umbilical arteries give off no branches, and the vein contains no valves, nor can any vasa vasorum be detected in their coats after they have left the umbilicus. The umbilical arteries increase in size after they leave the cord, to divide on the surface of the placenta. This is the only example in the body in which arteries are larger near their terminations than their origin, and the object of this arrangement is probably to effect a retardation of the current of the blood distributed to the placenta. The tortuous course of the vein probably compensates

1 Acad. des Sciences, April, 1859.

for the absence of valves, and moderates the flow of blood through it.'

Distinct knots are not unfrequently observed in the cord, but they rarely have the effect of obstructing the circulation through it. They no doubt form when the foetus is very small. They may sometimes also be produced in labor by the child being propelled through a coil of the cord lying circularly around the os uteri. The so-called false knots are merely accidental nodosities due to local enlargements of the vessels.

CHAPTER II.

THE ANATOMY AND PHYSIOLOGY OF THE FETUS.

It is obviously impossible to attempt anything like a full account of the development of the various foetal structures, or of their growth during intra-uterine life. To do so would lead us far beyond the scope of this work, and would involve a study of complex details only suitable in a treatise on embryology. It is of importance, however, that the practitioner should have it in his power to determine approximately the age of the foetus in abortions or premature labors, and for this purpose it is necessary to describe briefly the appearance of the foetus at various stages of its growth.

1st Month. The foetus in the first month of gestation is a minute gelatinous and semi-transparent mass, of a grayish color, in which no definite structure can be made out, and in which no head or extremities can be seen. It is rarely to be detected in abortions, being lost in surrounding blood-clots. In the few examples which have been carefully examined it did not measure more than a line in length. It is, however, already surrounded by the amnion, and the pedicle of the umbilical vesicle can be traced into the unclosed abdominal cavity.

2d Month. The embryo becomes more distinctly apparent, and is curved on itself, weighing about sixty-two grains, and measuring six to eight lines in length. The head and extremities are distinctly visible the latter in the form of rudimentary projections from the body. The eyes are to be seen as small black spots on the side of the head. The spinal column is divided into separate vertebræ. The independent circulatory system of the foetus is now beginning to form, the heart consisting of only one ventricle and one auricle, from the former of which both the aorta and pulmonary arteries arise. On either side of the vertebral column, reaching from the heart to the pelvis, are two

[ In some instances the disproportionate length of the vein causes the cord to assume a screwlike form, which may be very regular, as is exhibited to a remarkable degree by one in my possession, in which there are between thirty and forty turns. involving the whole funis, which is of average length in a straight line.-ED.]

large glandular structures, the corpora Wolffiana, which consist of a series of convoluted tubes opening into an excretory duct, running along their external borders, and connected below with the common cloaca of the genito-urinary and digestive tracts. They seem to act as secreting glands, and fulfil the functions of the kidneys before they are formed. Toward the end of the second month they atrophy and disappear, and the only trace of them in the foetus at term is to be found in the parovarium lying between the folds of the broad ligaments. At this stage of development there are met with in the human embryo, as in that of all mammals, four transverse fissures opening into the pharynx, which are analogous to the permanent branchiæ of fishes. Their vascular supply is also similar, as the aorta at this time gives off four branches on each side, each of which forms a branchial arch, and these afterward unite to form the descending aorta. By the end of the sixth week these, as well as the transverse fissures to which they are distributed, disappear. By the end of the second month the kidneys and supra-renal capsules are forming, and the single ventricle is divided into two by the growth of the inter-ventricular septum. The umbilical cord is quite straight, and is inserted into the lower part of the abdomen. Centres of ossification are showing themselves in the inferior maxillary bones and the clavicle.

3d Month. The embryo weighs from seventy to three hundred grains, and measures from two and a half to three and a half inches in length. The forearm is well formed, and the first traces of the fingers can be made out. The head is large in proportion to the rest of the body, and the eyes are prominent; the mouth is closed by the lips, and is separated by them from the nasal cavity. The umbilical vesicle and allantois have disappeared, and the alimentary canal is now situated entirely within the abdominal cavity. The greater portion of the chorion villi have atrophied, and the placenta is distinctly formed.

4th Month. The weight is from four to six ounces, and the length about six inches. The convolutions of the brain are beginning to develop. The sex of the child can now be ascertained on inspection. Hairs begin to be formed on the head. The muscles are sufficiently formed to produce distinct movements of the limbs. Ossification is extending, and can be traced in the occipital and frontal bones, and in the mastoid processes. The sexual organs are differentiated.

5th Month. Weight about ten ounces. Length, nine or ten inches. Hair is observed covering the head, which forms about one-third of the length of the whole foetus. The nails are beginning to form, and ossification has commenced in the ischium. The foetal movements are distinct, and in cases of premature delivery, may continue for some time after the birth of the child.

6th Month. Weight about one pound. Length, eleven to twelve and a half inches. The hair is darker. The eyelids are closed, and the membrana pupillaris exists; eyelashes have now been formed. Some fat is deposited under the skin. The testicles are still in the abdominal cavity. The clitoris is prominent. The pubic bones have begun to ossify.

7th Month. Weight from three to four pounds. Length, thirteen to fifteen inches. The skin is covered with unctuous, sebaceous matter, and there is a more considerable deposit of subcutaneous fat. The eyelids are open. The testicles have descended into the scrotum. Children born at this time may occasionally survive.

8th Month. Weight from four to five pounds. Length, sixteen to eighteen inches, and the foetus seems now to grow in thickness rather than in length. The nails are completely developed. The membrana pupillaris has disappeared.

Foetus at Term.-At the completion of pregnancy the foetus weighs on an average, six and a half pounds, and measures about twenty inches in length. These averages are, however, liable to great variation. Remarkable histories are given by many writers of foetuses of extraordinary weight, which have been probably greatly exaggerated. Out of 3000 children delivered under the care of Cazeaux at various charities, one only weighed ten pounds. There are, however, several carefully recorded instances of weight far exceeding this; but they are undoubtedly much more uncommon than is generally supposed. Dr. Ramsbottom mentions a foetus weighing sixteen and a half pounds; Cazeaux tells us of one which he delivered by turning, which weighed eighteen pounds and measured two feet one and a half inches; and the birth of one weighing twenty-one pounds has been recently recorded. Such overgrown children are almost invariably stillborn. The average size of male children at birth, as in after-life, is somewhat greater than that of female. Thus Simpson found that out of 100 cases the male children averaged ten ounces more in weight than the female, and half an inch more in length.

3

[Some mothers of average size never bear a foetus of even six pounds in weight, although begotten by a husband of full vigor. One of my patients bore a daughter of three and a half pounds; a second of two and three-quarters; and a son of five and a half pounds. The first daughter has given birth to a girl of one and a half pounds, now living at the age of two. The second died at eight months; and the son is a vigorous youth of sixteen. Such small children sometimes grow to very large size and live to advanced age, as witness the fact that one in this city became a large, tall woman, and died at the age of eightyseven years.-Ed.]

A newborn child at term is generally covered to a greater or less extent with a greasy, unctuous material, the vernix caseosa, which is formed of epithelial scales and the secretion of the sebaceous glands, and which is said to be of use in labor by lubricating the surface of the child. The head is generally covered with long dark hair, which

1 Brit. Med. Journ., Feb. 1, 1879.

2 Probably the largest foetus on record was that of Mrs. Captain Bates, the Nova Scotia giantess, a woman of seven feet nine inches, whose husband is also of gigantic build, reaching seven feet seven inches in height. This child, born in Ohio, was their second, and was lost in its birth, as no forceps could be procured of sufficient size to grasp the head. The fetus weighed twenty-three and three-quarter pounds, and was thirty inches in length. Their first infant weighed eighteen pounds. We have had children born in this city (Philadelphia) at maturity and live, that weighed but one pound. The well-remembered "Pincus baby" weighed a pound and an ounce. (Harris, note to 3d American edition).

3 Selected Obstetrical Works, p. 327.

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