232 



HUMAN EMBRYOLOGY AND MORPHOLOGY. 



well as the vitelline comes to be poured into the liver. The left 

 umbilical vein within the body remains permanently ; when its 

 terminal part is broken up by the outgrowth of the liver it 

 becomes united with the uppermost of the transverse communica- 



right duct, 

 of Cuuier} 



right umb. vein 

 in somato-pleure 



pericardium 



sinus uenosus 

 sept, transuersum. 

 rt. uit. uein on yolk sac. 



left umb. vein 



united umb. veins 

 cord 



chorion 



■£TT? 



Fig. 190.— Diagram of the Right Umbilical Vein in an embryo of 3 weeks, before the 

 outgrowth of the Liver Bud. (Modified from His.) 



tions between the right and left vitelline veins, which, as already 

 mentioned, form the part of the portal vein within the transverse 

 fissure of the liver. The left umbilical vein thus comes into com- 

 munication with the ductus venosus (see Figs. 188 and 189). 



DEVELOPMENT OF THE HEART. 



The Heart. — In the 2nd week, while the embryo is still in 

 the blastoderm stage, a contractile tube appears in the splanchno- 

 pleure on each side (Fig. 191). Each tube receives blood from 



