lOO 



THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



vein, which courses cephalad and in earlier stages connects with the sinusoids 

 of the hver. The portal vein then bends sharply to the right, dorsal to the duo- 

 denum, and, in the course of the right vitelline vein, passing between the dorsal 

 and ventral pancreas to the right of the duodenum, it soon enters the liver and 

 connects with the liver sinusoids. The portal trunk is thu,s formed by persisting 

 portions of both vitelhne veins, and receives a new vessel, the superior mesenteric 

 vein. The middle portions of the primitive vitelhne veins are connected with the 



Spiii'il cord 

 Ant. cardinal vein 



Cervical iiniis 



Pericardial cavily 



Atrial junction sinus vcnosm 

 Sinus vcnosus 

 Right vitelline vein 

 Live 



Large venous sinusoid, of live 



Hepatic diverticulum (cul 

 Yolk stalk 



Portal vein 



Cephalic linili 



intestinal liiof> 



Right umbilical vein 



Vitelline arkiy 



Caudal limh 

 intesliiial loop 

 Right umbilical aitu \ 



Dot su/ aojUi 



P^olochayd 

 . 1 )\l . ('aedinal 

 vein 



Pharynx 



Pericardial 



cavily 



Left common 

 cardinal vein 



Lefl horn of sinus venosus 



Left vitelline vein 

 Ductus venosus 

 A nl. limh bud 

 Inf. vena cava 

 Dorsal pancreas 

 I.cfl vilelline vein 

 Common vitelline vein 



Left umbilical vein 



Slip, mesenteric vein 

 Left umbilical artery 

 Post, limb bud 

 Spinal cord 



Fig. 102. — Reconstruction in ventral view of a 6 mm. pig embryo to show the \'itelline and umbilical 

 veins, the latter opened (original drawing by Dr. K. L. Vehe). X 22. In the small orientation figure 

 (cf . Fig. 105) the various planes are indicated by broken lines — * *. 



network of liver sinusoids. Their proximal vitelhne trunks drain the blood from 

 the liver and open into the sinus venosus of the heart. The right member of this 

 pair is much the larger (Fig. 100) and persists as the proximal portion of the infe- 

 rior vena cava. For the development 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. 

 102 and 105) . Before the allantoic stalk enters the body, the umbiUcal veins sepa- 



