n8 



THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



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

 Umbilical Arteries (Fig. 109). As the posterior half of the embryo is curved in the form 

 of a half circle, sections caudal to the liver, like 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, 

 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 dorsal 



Spinal cord 



Notochord 

 Kpost card. Vein 



Dorsal aorta 

 R.sub. card, vein 



Mesentery 



Cephalic limb 

 of intestine 



R.bmbilical Vein 



Caudal Jitnb of 

 intestine 



Vein 

 Tail 



Lower limb bud 

 Mesonephric ducf 



Dorsal aorta 

 Spinal cord 



Spina.1 nerve 



Postcard. vein 



Mesonephros 

 L.sub.card. Vein 



Lviteltine Vein 

 Lumb'ili'cal Vein 



Coehtn 



Vein 



Rectum 

 Meslubule 



Mes.seqmerii 



FlG. 109. 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. Mes. tubule, 

 mesonephric tubule; R. post. card, vein, right posterior cardinal vein. 



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 intes- 

 tine transversely), and also sections of the vitelline artery and veins. In the lateral body walls 

 ventral to the mesonephros occur the umbilical veins. The left vein is large and cut length- 

 wise. The right vein is cut obliquely twice. 



