no THE STXJDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



connects the liver with the ventral body wall he on each side the umbilical veins, the left being 

 the larger. Between the veins is the extremity of the hepatic diverticulum. The body wall is 

 continued ventrad to form a short umbilical cord. 



Transverse Section at the Level of Origin of the Vitelline Artery and Umbilical 

 Arteries (Fig. 114). — As the posterior half of the embryo is curved in the form of a half 

 circle, sections caudal to the liver, hke this one, pass through the lower end of the body 

 at the level of the posterior limb buds. Two sections of the embryo are thus seen in one. 



Spinal rd 



Nolniiioi I 

 R. post, cardinal vein 



Dorsal dorla 

 R. subcardinal vein 



Mescnkiy 



Cephalic limb of inlcslin 

 R. umbilical vein 



Caiidal limb of inlesline 



R. umbilical vein 



Tail 



Lower limb bud 

 Mesonephric duel 



Dorsal ami 



S final ivid 



Spinal nerve 



Post, cardinal vein 



ilesonephros 



L. subcardinal vein 



L. vitelline vein 

 L. umbilical vein 



/-. umbilical vein 

 Rcetitm 



Mesonephric tubule 

 Mesodermal segment 



Fig. 114. — Transverse section of a 6 mm. pig embryo at the level of the origin of the vitelline 

 artery. The lower end of the section passes through the posterior limb buds. X 26.5. 



their ventral aspects facing each other and connected by the lateral body wall. In the dorsal 

 part of the section the mesonephroi are prominent with large posterior cardinal veins lying dor- 

 sal to them. The trunk of the vitelline artery takes origin ventrally from the aorta. It may 

 be traced into the mesentery, and through it into the wall of the yolk sac. On either side of 

 the vitelline artery are the subcardinal veins, the right being the larger. In the mesentery 

 may be seen two sections of the intestinal loop (the small intestine being cut lengthwise, the 

 large intestine transversely), and also sections of the vitelline artery and veins. In the lateral 



