Identifier: systemri01hirs (find matches)
Title: A system of obstetrics
Year: 1888 (1880s)
Authors: Hirst, Barton Cooke, 1861-1935
Subjects: Obstetrics
Publisher: Philadelphia, Lea brothers & co.
Contributing Library: Yale University, Cushing/Whitney Medical Library
Digitizing Sponsor: Open Knowledge Commons and Yale University, Cushing/Whitney Medical Library

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rom the chorion l?eve, theprocesses on its surfaces do not completely abort. It becomes, as thetime of birth approaches, more and more closely united with thereflexa, till the union between the two is so close that their exactboundaries cannot be made out. The umbilical vesicle (uv), althoughit becomes greatly reduced in size and flattened, persists in a recogniz-able form till the time of birth. ••A- the embryo enlarges the space between the decidua vera and decidua reflexa becomes reduced, and finally the two parts unite During the whole of pregnancy the decidua vera can, however, be dis-tinguished by its structure, and remains highly vascular. The deciduareflexa becomes non-vascular, and fuses, as has been stated, on one sidewith the chorion and on the other with the vera. The membrane result-ing from its fusion with the latter becomes thinner and thinner as preg-nancy advances, and is reduced to a thin layer at the time of birth. 134 DEVELOPMENT OF THE EMBRYO. Fig. 82. ( dg^m^
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(Vr >m Balfour, after Turner.) A, placenta In it- most generalised form: B, structure of placentastructure of placenta ol structure of placenta of fox ; E, structure of pla- centa of cai; F, structure of placenta f sloth : on the right Bide of the figure the Bat mater-nal epithelial cells are shown fa attu: on the left ride they are removed, and the dilated THE EARLY STAGES OF DEVELOPMENT. 135 The Placenta.—The human placenta is so highly specialized a struc-ture that to understand it requires some previous study of simpler formsof the organ. The placentae of the higher mammals fall into two great groups—deciduate and non-deciduate. In the deciduate type the connectionbetween the foetal and maternal structures is so close that part of theuterine mucous membrane comes away with the after-birth; this is notthe case id non-deciduate forms. There are several subsidiary varietiesof both these main kinds of placentae, known from their shape andarrangement as discoidal, zonary

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