ioS 



THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



sinusoids. Their proximal vitelline trunks drain the blood from the liver and 

 open into the sinus vcnosus of the heart. The right vitelline trunk is much the 

 larger and persists as the proximal portion of the inferior vena cava (for the de- 

 velopment of the portal vein see Chapter IX). 



The umbilical veins, taking their origin in the walls of the chorion and allan- 

 toic vesicle, he caudal and lateral to the allantoic stalk and anastomose (Figs. 

 97 and 99). Before the allantoic stalk enters the body, the umbilical veins sepa- 



Spina! cord 

 Ant. cardinal vein 



Cervical sinus 



Pericardia! cavity 



Atrial junction sinus- 

 venosus 



Sinus venosns 

 Right vitelline vein 



Liver 



Large venous sinusoid 



of Liver 



Hepatic diverticulum 



{cut) 



Yolk-stalk 



Portal vein 



Cephalic limb 

 intestinal loop 



Right umbilical vein 

 Vitelline artery 



Caudal limb 

 intestinal loop / 

 Right umbilical artery 



Dorsal aorta 



Kolochord 



Ant. cardinal vein 



Pharynx 



Pericardial cavity 



Left common cardinal 

 vein 



-Left horn of sinus 

 veuosus 

 Left vitelline vein 



Ductus veuosus 



Ant. limb bud 



Inf. vena cava 



Dorsal pancreas 



Left vitelline vein 



Common vitelline vein 



Left umbilical vein 



Sup. mesenteric vein 



Left umbilical artery 



Post, limb bud 

 Spinal cord 



Fig. 97.— Reconstruction in ventral view of a 6 mm. pig embryo to show the vitelline and umbilical 

 veins, the latter opened (original drawing by Mr. K. L. Vche). 



rate and run lateral to the umbilical arteries. The left vein is much the larger. 

 Both, after receiving branches from the posterior limb buds and from the body 

 wall, pass cephalad in the somatopleure at each side. Their course is hrst 

 cephalad, then dorsad, until they enter the liver. The left vein enters a wide 

 channel, the ductus venosus, which carries its blood through the liver, thence to 

 the heart by way of the right vitelline trunk. The right vein joins a large sinu- 

 soidal continuation of the portal vein in the liver. This common trunk drains 

 into the ductus venosus. 



