io8 



THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



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

 open into the sinus venosus 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, lie caudal and lateral to the allantoic stalk and anastomose (Figs. 

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



Spinal cord 

 Ant. cardinal vein 



Cervical sinus 



Pericardial cavity 



Atrial junction sinus- 



venosus 



Sinus venosus 



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 



Notochord 



Ant. cardinal vein 



Pharynx 



Pericardial cavity 



Left common cardinal 

 vein 



-Left horn of sinus 

 venosus 

 Left vitelline vein 



Ductus venosus 

 Ant. limb bud 

 Inf. vena cava 

 Dorsal pancreas 

 Left vitelline vein 

 Common vitelline vein 



Left umbilical vein 

 Sup. mesenteric vein 



umbilical artery 

 Caudal limb 

 intestinal loop 

 Right umbilical artery 



Dorsal aorta ' 



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. Vehe). 



Post, limb bud 

 Spinal cord 



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 first 

 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. 



