124 



THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



anastomose just caudal to the origin of the superior mesenteric artery and the 

 posterior cardinals are interrupted at this level. The proximal portions of the 

 posterior cardinals open into the common cardinal veins as in the 6 mm. embryo. 

 Of the two subcardinal veins, the right has become very large through its con- 

 nection with the right posterior cardinal vein and the common hepatic vein, and 

 now forms the middle portion of the inferior vena cava. For the development 

 of this vein, see Chapter IX. 



Nolmhonl 

 Pliai\ii\ 



Pericardial 

 Sinus venosiis 



Inf. vena cava 



Spinal cord 



Anl. lardinal vein 

 Esophagus 



ppcr limb 



Cainmon car- 

 di)ial vein 



Portal !' 

 Ventral pancri 

 Ca 



L. vitelline ii 

 Small in 



Diirlus venosus 



Liver 



I'yiaric stomach 



llcpalic diverticulum 



Darsal pancreas 



Duodenum 



umbilical vein 



nlois 



Fig. 127. — Reconstruction of a 10 mm. pig embryo to show the umbilical and vitelline veins from 

 the ventral side, x indicates sinusoidal connection between left umbilical vein and portal vein. X 15. 

 In the small orientation figure (c£. Fig. 123) the various planes are indicated by broken lines — 



The umbilical veins (Figs. 126 and 127) anastomose in the umbilical cord, 

 separate on entering the embryo, and course cephalad in the ventro-lateral body 

 wall of each side to the ventral lobe of the liver. The left vein is much the 

 larger, and, after entering the liver, its course is to the right and dorsad. After 

 connecting with the portal vein, it continues as the ductus venosus and joins the 

 proximal end of the inferior vena cava. The smaller right umbilical vein after 

 entering the liver breaks up into sinusoids. It soon atrophies, while the left vein 

 persists until after birth. 



The Vitelline Veins. — Of these, a distal portion of the left and a proximal 



