within them. The maternal and fœtal blood pass by or over each other in capillary streams, but without actually intermingling; the tufts of the chorion, it is to be observed, are not sunk into the sinuses of the uterine veins, but into the tortuous and greatly enlarged uterine glands. Both parts of the placenta are subsequently so intimately blended together, without, however, any departure from the fundamental arrangement, that they cannot be separated; but the maternal part may be detached by laceration of the connecting vessels and fibres of the developed part of the uterine glands; in fact, the uterus in this place is stripped of its membrane, which, with its glands, is afterwards regenerated. (Entwickelungsgeschichte, &c. pp. 114, 115).

In this description, we have directed attention to the important circumstance that, after development has advanced to a certain extent, the decidua uteri readily tears off. This explains what happens in the case of human gestation, and especially shows how the decidua uteri may be raised in dissection from the uterus, as if it were a layer distinct from the mucous membrane.

In proceeding to the investigation of the human placenta, there is doubtless much more difficulty in analysing its minute structure, though the main facts are fully determined. There are some important points in which it strongly contrasts with the placenta of mammalia; and we are ourselves of opinion that, taking these differences into consideration, it may be predicted that ultimately the mode of formation and constitution will be found to be essentially the same in man and animals. The principal differences to which we allude are these: that in the human female there is an additional element concerned, the decidua reflexa, which has no certain existence in animals; and secondly, that in man, the fœtus is larger than in any animal having a single placenta, that has hitherto been investigated, a circumstance which must modify the character of the placenta, though it may not alter its essential constitution. In the valuable contribution to which we have alluded, Professor Weber mentions several circumstances, from which he seems to doubt whether the human placenta is formed according to the same principles as that of the cat and dog: the most important of these circumstances we shall now quote, both because they bear upon the point in question and also because they convey several important facts connected with the structure of the placenta. The peculiar enlargement of the ducts of the uterine glands into the wide and folded pouches already described, has not yet been seen by Dr. Weber in the human female; nor in a gravid uterus of the tenth week could he discover that the branched tufts of the chorion had pushed into the openings of the utricular glands; and moreover, the simple figure of the utriculi of the human uterine glands did not correspond to the infinitely ramified and divided tufts of the chorion. It cannot, therefore, be assumed as proved, that in man the tufts of the chorion grow into the utriculi of the uterine glands, as they certainly do in the dog. Again, as man is distinguished by exclusively having a decidua reflexa, so a difference may exist as to the nature and formation of the placenta. Several other subordinate distinctions are also pointed out; such as, that the placenta uterina of the human female is distinguished in this-that the coarse vascular rete carrying the maternal blood, and which penetrates through the whole placenta, consists

1847]

:

Bischoff on Human Decidua.

15

of canals having a diameter fifteen times larger than the capillaries that bring the maternal blood into the placenta of the dog, whilst the walls are much thinner that the other element of the placenta, the tufts of the chorion, carrying a very rich rete of minute embryonic capillary vessels, form in the dog membranes and folds, in man, on the contrary, small trees with cylindrical branches and twigs; that in the human placenta there are, in the usual sense of the word, no capillary vessels, but only vessels of to of a line in diameter (colossal capillaries or veins), and that the arterial branches to line in diameter, which conduct the maternal blood out of the uterus into the placenta, do not divide themselves repeatedly into branches, but form, in their passage into the placenta, a coil (glomus arteriosus), which consists of a single artery twisted here and there, and which at length prolongs itself directly into the network of those colossal capillary vessels or veins which penetrate through the whole placenta: lastly, that whilst it happens both in man and in the dog that the vessels carrying the maternal blood come into intimate contact with those carrying the embryonic blood, yet, in the latter, it happens that the vessels carrying the maternal blood into the placenta are individually developed between the membranes and folds of the tufts of the chorion, and are covered by them; in the former, on the contrary, the branches and fibres of the tufts of the chorion are covered by and developed in the walls of the very wide and thin-walled maternal blood-vessels, which, filling up the intervals between them, insinuate themselves on and so surround the tufts. Professor Weber finishes this summary by remarking that, if it should be shown hereafter that the tufts of the chorion in man, as in the dog, grow into the utriculi of the uterine glands, and thus fill them up, it would thence follow that the branches and terminal fibres of those tufts, would acquire a thin and adherent covering, derived from the walls of the uterine glands.-Müller's Archives, 1846, p. 424.

In opposition to the objections set forth by Weber, but evidently without any certain conviction of their truth, we would again refer our readers to the account of Dr. Sharpey, and especially to the figures illustrative of the uterine glands of the bitch, and of the same organs in the human subject. We shall also now append the most recent views of Professor Bischoff on this important point. In the work before alluded to (Müller's Archives for 1846, p. 111), a very instructive case of early pregnancy is related by this admirable observer.

From the facts stated, there is no doubt that impregnation had occurred within 14 or 21 days before death. The case was that of a married woman, aged 31, who had borne eight children, and who destroyed herself by drowning.

"The inner surface of the cavity of the uterus had an appearance quite different from the usual one, and which became very distinct when the organ was placed in water; it had, namely, a very delicate and apparently tufted condition, and this was particularly distinct upon the cut borders. The surface itself, if viewed from above, appeared as if finely perforated; or rather, as if closely covered or beset with small white points, which, upon the section, were perceptible as the free ends of the apparently white tufts. These little tufts, however, were not such in reality; for, firstly, they were all connected together by means of a semi-transparent mass; and further, it was easy for a person expe

rienced in these investigations to perceive, by employing magnifying powers, that these apparent tufts were small glandular canals or pouches (drüsenschlauche) 11⁄2 to 2 Paris lines long. The analogous formations of the dog, the cow, the sow, &c. being known, I could not remain in any doubt, their nature was apparent at the first glance they were the same uterine glandular canals which I had sought for in vain in the unimpregnated condition (of the human uterus), but which here showed themselves quite clearly and distinctly, even to the naked eye.” "Now, as I have already entirely convinced myself that in the dog (herein agreeing with Sharpey) these glandular canals, expanded into flask-shaped pouches, take up the tufts of the chorion, to form together with these in the rapid progress of development, the so-called decidua in the bitch's ovum, so I hold it to be no longer doubtful that, in the human female, a precisely similar disposition takes place. These glands seem to be very small and indistinct in the unimpregnated state; but after conception they grow rapidly, and an exudation also occurring from the surface of the uterus, they in a manner grow into this exudation, and the two together then form the decidua vera; and, at that part where, owing to the application of the allantois, the tufts of the chorion become further developed, the placenta. The decidua, therefore, is in fact, if not exactly the membrana, at least the stratum uteri internum evolutum ; and, as such, a formation is present, partly as a product of development and partly as a new formation. At birth, a real casting off of the inner (mucous) layer of the uterus takes place; but it is to be presumed that the fundamental part of the glandular canals, namely, their cæcal extremities, which project against the fibrous coat, are left behind."-L. c.

In this account there is one circumstance to which attention should be particularly directed, as it will explain one of the many sources of error by which the formation of the decidua vera has become so involved and obscured. We allude to the circumstance, that when the uterine glands become enlarged, they give to the free surface of the mucous membrane of the uterus, what would not have been expected à priori, a peculiar tufted appearance, and which has consequently been often mistaken for true villi. For the rest, it is very satisfactory to find the important researches of Weber and Sharpey concerning the uterine glands, thus confirmed by an anatomist, who probably, owing to his extended and successful researches, was the best qualified in Europe to offer an opinion.

There is still some uncertainty concerning the nature of the decidua reflexa; this is of the less consequence, as it is altogether a secondary part, and is absent in animals. We have already said that it has an origin totally distinct from that of the decidua vera. Dr. Sharpey suggests, without wishing to affirm anything positively, that it may consist of exuded lymph, which covers the minute ovum on its entrance into the uterus, either entirely or on that part of its surface which does not adhere to the uterus. Mr. Goodsir, who has satisfied himself that the decidua reflexa is a distinct formation, offers an explanation of its origin in accordance with his views of the process of nutritive absorption in the alimentary canal; namely, that this covering, which he proposes therefore to call the cellular decidua, is formed of cells passing off from the uterine glands, and which surround the ovum when it enters the cavity of the uterus. Connected with this view of the origin of the d. reflexa, he has a theory that this structure, by the powers of its active cells, nourishes the ovum after this has exhausted the supply provided in the ovary, and that it thus performs the same part in the gestation of the mammal, which, in the egg of the oviparous animal, is effected by the albumen.

1847]

Hunterian Doctrines erroneous.

17

In the plates illustrative of development published by Dr. Erdl, there is a scheme representing the formation of the decidua reflexa (Erster Band, Zweiter Theil, Tab. 2, fig. 8), which is altogether too mechanical; and in the brief description of the plates, the author gives what is certainly an erroneous account of the production of the above layer, inasmuch as he states it to be nothing else than the prolongation over the ovum of that part of the decidua uteri which he affirms, but again erroneously, extended, prior to the descent of the ovum, over the orifice of the Fallopian tube. Upon this point Dr. Bischoff properly remarks, that as we are speaking of a most minute body, of the 1-12th of a line in diameter, all mechanical explanations of the way in which the ovulum becomes covered by the decidua reflexa, must fail of necessity; he himself considers the question to be undecided, and to require further research.

We have been led further into detail than we had designed; but as no true or clear idea of the structure of the placenta can be formed, without the relations of the ovum and uterus are definitely made out, it is hoped this consideration will prove a sufficient apology for the extent of the foregoing observations. Those who have carefully followed the account now given, will find a cloud of doubts and difficulties removed; and by comparing especially the critical observations of Weber upon the reciprocal relations of the various maternal and embryonic vessels and membranes contained in the placenta, with the accounts given by those writers, who have discovered many isolated facts connected with this body, often, however, mixed up with error, much that before was confused, apparently even contradictory, and therefore most unsatisfory, will become clear and comprehensive. The account of J. Hunter is certainly the most important of all the older histories of the placenta; and but for one pervading error, would probably long since have conducted his successors to the true anatomy. The error to which we allude is that Hunter, led away by his great principle concerning the effusion and organization of fibrin, regarded the decidua (both the vera and reflexa) as formed by an effusion of coagulable lymph, and which, like the effused fibrin poured out into any of the cavities of the body consequent upon the introduction of an extraneous living part, a comparison made by Hunter, became subsequently organised and vascular by the prolongation of vessels from the inner surface of the uterus.* Another error also occurs in this account, namely, that the ma

It is interesting to compare the account given by Hunter of the first changes induced in the uterus as the result of conception, with the late researches which we have noticed above. In a case where impregnation had occurred within one month before death, the inner surface was found covered with a pulpy substance in its thickest part forming a layer line thick, and " evidently formed by coagulated blood;" this substance was continued across the cervix, thus closing the cavity of the uterus, and also extended some way into the Fallopian tubes. "When the inner surface of the cavity of the uterus was examined with a magnifying power, it was found extremely vascular and dotted with innumerable whitish spots, too small to be seen by the naked eye." There is no doubt that these "whitish spots" were the orifices of the enlarged uterine glands filled with an abundant epithelium. We have quoted the authority and description of John Hunter, without at all alluding to the dispute between him and Dr. W. Hunter as to priority of discovery.

NEW SERIES, NO. XI.--VI.

C

ternal blood carried into the placenta by the curling arteries was there deposited in cells, from which it was said to be returned by channels ultimately leading into the uterine sinuses. This view was finally adopted by Mr. Owen, after he had for a time received as correct Dr. R. Lee's account. He found, on examining a gravid uterus of the ninth month, that the uterine veins were continuous with wide channels, passing obliquely through the decidua into the placenta, which "decidual canals," as they are here called, became diffused through the fine spongy and cellular substance which every where surrounds and supports the foetal capillaries, and at length penetrated to the surface of the placenta. This distinguished physiologist concluded that "the placental intercommunication between the fœtus and the mother, in the human subject and the quadrumana, is carried on by the contact of the foetal capillaries with maternal extravasated blood; while in ruminants, the mare and the sow, it takes place by the apposition of capillaries to capillaries, and the two parts of the placenta, namely the foetal and maternal, can be separated. In the feræ and rodentia there appears to be an intermediate structure."

The first correct view of the vascular arrangement of the placenta was taken by E. H. Weber, so long ago as 1832; and as the account given by that admirable anatomist is in itself essentially true, and has laid the foundation of all later researches, we are desirous of briefly submitting it to the notice of our readers. He first accurately describes the entrance of the uterine arteries and veins into the placenta, by passing obliquely through the decidua vera, thus confirming the fundamental fact ascertained by Hunter, but which has at various times been called in question. He notices the fact that, the coats of these maternal vessels become, on entering, extremely thin, and are therefore easily lacerated. The true relations existing between the maternal and the fœtal portions of the placenta are then, for the first time, thus accurately determined :-"The foetal part of the placenta consists, in man, of the multitudinous arborescent tufts of the chorion, which project into the canals of the widely-dilated veins filled with the maternal blood; these latter vessels pass from the inner surface of the uterus through the decidua vera, and penetrate throughout between the tufts of the fœtal portion of the placenta, and thus form a large network." After pointing out the appearances that doubtless deceived Hunter and his successors, as to the existence of cells, namely, that the uterine veins, where lodged between the tufts of the chorion, losing their cylindrical form, owing partly to the extreme tenuity of their walls and partly to their disposition, have the aspect rather of interstices and passages than of veins, Professor Weber thus explains the true structure: "it occasionally happens, however, that we are so fortunate as to find a place where it can be seen in what manner the veins are related to the tufts. At the borders, namely, of the placenta and sometimes in its substance, entering uterine veins are found, into the interior or cavities of which a small tuft of the fœtal portion of the placenta here and there projects, whilst the vein still has, in other respects, entirely the characters of a definitely limited canal with smooth internal parietes. We can in such places convince ourselves, that these tufts of the placenta fœtalis, thus projecting into the interior of the veins, do not pass through an actual perforation in the vein, but that the inner extremely thin venous membrane at the place where the tuft pushes