XII.J SUPRA-RENAL BODIES. 413 



receives branches from this organ near its anterior exit. 

 The main trunk is however never completely aborted, as 

 in the embryos of other types, but remains as the ductus 

 venosus Arantii. 



With the development of the placenta the allantoic 

 vein becomes the main source of the ductus venosus, 

 and the viteUiue or portal vein, as it may perhaps be 

 now conveniently called, ceases to join it directly, hut 

 falls into one of its branches in the liver. 



The vena cava inferior joins the continuation of the 

 ductus venosus in front of the liver, and, as it becomes 

 more important, it receives directly the hepatic veins 

 which originally brought back blood into the ductus 

 venosus. The ductus venosus becomes moreover merely 

 a small branch of the vena cava. 



At the close of foetal life the allantoic vein, becomes 

 obliterated up to its place of entrance into the liver; 

 the ductus venosus becomes a solid cord — the so-called 

 round ligament — and the whole of the venous blood is 

 brought to the liver by the portal vein. 



Owing to the allantoic (anterior abdominal) vein 

 having merely a fcetal existence an anastomosis between 

 the iliac veins and the portal system by means of the 

 anterior abdominal vein is not established. 



The supra-renal bodies. These are paired bodies 

 lying anterior to the kidneys and are formed of two 

 parts, (1) a cortical and (2) a medullary portion. They 

 first appear in the Rabbit on the 12th or 13th day of 

 gestation, and arise as masses of mesoblast cells lying 

 between the aorta and the mesentery and to one side of 

 the former. On the 14th day they are well marked, 

 and lying dorsal to them is another mass of cells which 



