348 THE CIRCULATION OF THE BLOOD. [CHAP. XXVIII. 



end in the Malpighian tufts, whence the blood is taken up by the 

 efferent veins, which quickly break up like arteries into another 

 capillary plexus surrounding the uriniferous tubes, and this plexus 

 gives origin to the radicles of the renal or emulgent veins. 



The hepatic portal circulation, however, has several points of 

 communication with the systemic veins or the inferior vena cava ; 

 and thus it happens, when from disease of the liver a considerable 

 portion of the portal system of that organ is obstructed or obliter- 

 ated, that a part of the blood from the intestinal canal finds its 

 way into tributary veins of the cava, and returns by that route to 

 the right side of the heart. The points of communication are 

 between the veins of the cava (left renal) and of the intestines, 

 especially the colon and the duodenum, and between the inferior 

 mesenteric and the hemorrhoidal veins, a fact which explains the 

 frequent occurrence of hemorrhoids in obstructions of the liver; 

 also between superficial branches of the portal veins of the liver, 

 and the phrenic veins, as pointed out by Kiernan. 



Bernard states that immediately after the portal vein has entered 

 the liver, and sometimes before, a certain number of branches are 

 given off from it, which, entering the liver, some superficially, others 

 more deeply, form communications with the vena cava. 



Of the Foetal Circulation. In the foetus in utero the course of 

 the circulation \& greatly modified, by reason of the inaction of the 

 lungs as aerating organs, and the consequent imperfect attraction of 

 the blood to them. During intra-uterine life, the aeration of the 

 fetal blood is effected by the placenta, a highly vascular organ, in 

 which the fcetal blood is brought into a very close relation to the 

 maternal blood as it circulates through the wall of the uterus. 

 The placenta, therefore, is in effect the lung of the foetus, and bears 

 a corresponding relation to its circulation. 



A large portion of the fcetal blood is carried to the placenta 

 through the umbilical arteries, which are continuations of the 

 trunks of the internal iliac arteries escaping from the body of the 

 foetus through the umbilicus. From the placenta the blood is re- 

 turned to the foetus by the umbilical vein, which is bound up with 

 the umbilical arteries in the umbilical cord, and enters the body of 

 the foetus at the navel. From this point the umbilical vein passes 

 upwards and to the right side under the liver, in its longitudinal 

 fissure, and at its transverse fissure it joins the sinus of the vena 

 porta, through which most of its blood is distributed to the liver. 

 One large branch, however, follows the course of the original 

 trunk in the posterior part of the longitudinal fissure, and opens 



