. Manual of antenatal pathology and hygiene : the foetus. ally prepared andextra-corporeal organ (the placenta) for purposes of oxygenation andother less understood chemical changes. This entails simply thepresence of an efferent vessel (or vessels) to carry the blood to theextra-corporeal organ and of an afferent vessel to bring it back may roughly compare it to a coal-pit connected with a railwaysystem: to the pit there runs a line of rails along which truckscarrying cinders and rubbish pass, and along another line come backagain the trucks filled with coal. But the presence of this
. Manual of antenatal pathology and hygiene : the foetus. ally prepared andextra-corporeal organ (the placenta) for purposes of oxygenation andother less understood chemical changes. This entails simply thepresence of an efferent vessel (or vessels) to carry the blood to theextra-corporeal organ and of an afferent vessel to bring it back may roughly compare it to a coal-pit connected with a railwaysystem: to the pit there runs a line of rails along which truckscarrying cinders and rubbish pass, and along another line come backagain the trucks filled with coal. But the presence of this accessoryextra-corporeal system of vessels entails some slight modifications of 128 ANTENATAL PATHOLOGY AND HYGIENE the circulatiou iuside the fcetal body, for the blood coming from theplacenta has to be distributed to the various parts of the body insuch a way that all shall share in it but, some to a greater extentthan others. To continue the comparison wliich has been instituted,the coal from the coal-pit has not only to be sent all over the railway. Fig. ::=.- .lue of fcetal eu-eulatiou (after Prever\ system, but it has to be sent in special amoimt and of a specialquality to the parts where the traffic is most and the speed of thetrains greatest; in order to carry out this object, special hues haveto be laid and special depots built. It will be convenient to considertirst the extra-corporeal part of the fa?tal circulation, aud second theintra-corporeal. FCETAL CIRCULATION 129 The venous blood is carried from the fwtus to the placenta bythe two umbilical arteries, each of which arises from the internalihac artery of the same side. In the intra-abdominal part of theircourse they are known as hypogastric arteries, and in the extra-abdominal or funic part as umbilical arteries. Through themimpure foetal blood is transmitted to their ultimate ramifications inthe capillaries of the yilli, where it may be said to be brought, if notinto touch with, at any rate almost within sight
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