A study of the human placenta, physiological and pathological / by Thomas Watts Eden.

  • Eden, Thomas Watts, 1864-1946.
Date:
[1894?]
Catalogue details

Licence: Public Domain Mark

Credit: A study of the human placenta, physiological and pathological / by Thomas Watts Eden. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    as simple- ectodermal buds, which grow by a process of repeated branching, and are arborescent when fully formed. In Keichert’s ovum, the villi were not found covering the entire surface (36), His found them fairly evenly distributed (13). There is, at this period, no trace of the differentiation of a special area to form the placenta. Many of the villi are vascularised in all parts of the ovum. This represents all that is at present known of the development of the chorionic membrane in man. It is closely related to the develop- ment of one of the maternal envelopes of the ovum, the decidua reflexa. In a human ovum of the end of the second week, the reflexa has closed completely over the ovum, and the chorionic villi are embedded in it, but so lightly that the two are readily separable. Observations are greatly needed as to the precise relations of the villi to the decidual tissues at this period; beyond the fact that there is a delicate union between them we know nothing. It is, however, a fact of great physio- logical importance, that, by the end of the second week, the foetal and maternal vessels are brought into close relations by the embedding of the villi in maternal tissues, thus forming what is practically a simple type of placenta in which the wall of the entire ovum is concerned. The conclusion seems inevitable that the chief function of the decidua reflexa is associated with the nutrition of the ovum. It is a highly vascular membrane, richly supplied with glands, and the foetal vessels enclosed in their delicate villi become buried in its substance. An interchange by osmosis between the maternal and foetal blood must inevitably result. No doubt a secondary function of the reflexa is to support the rapidly growing ovum. At the end of the second week, therefore, we have in the human ovum a simple form of diffused placenta, corresponding to that which is met with in the sow, the mare, the cetacea, etc. In the mammalia generally the umbilical vesicle plays a comparatively unimportant part in the nutrition of the embryo; and early provision is therefore made for the direct transmission of nutrient materials from the blood of the mother to the embryo. This provision, as we have seen, is found in the embedding of the fcetal villi in maternal tissues. In this manner the fcetus is nourished, while time is gained for the development of the more highly specialised discoidal placenta. Text-books usually state that the placenta does not appear, in the case of human ovum, till the end of the second month. I am disposed to believe, from specimens which I have examined from the middle of the second month, that the placenta is at that time already in an advanced stage of development. The point, however, is not of great importance, for the development of the discoidal placenta in man, simply consists in the specialisation of a part of the chorion to perform the work which, in earlier stages, is done by the whole of it. At the placental site the villi increase very much in size and number, and hi the complexity of their branchings; at the same time important changes, to be afterwards described, occur in the