ANOMALIES OF THE VITELLINE VEINS 105 



Elze has shown that the superior mesenteric vein is a well-defined 

 stem which empties into the spiral vessel formed from the peri- 

 intestinal rings. The place of junction comes to lie on the left 

 side of the intestine, both in human embryos (Elze) and in pig 

 embryos (Lewis, Thyng). In other words it has shifted ventrally, 

 and the mesenteric vein appears to join the left half of the lower 

 peri-intestinal ring. Thus at the stage shown in His's figure, 

 when the spiral vein has been formed from the peri-intestinal 

 rings, the veins which unite near the intestine are the superior 

 mesenteric vein and the fused vitelline trunk. On the other hand, 



,V.Ar 



vu 



Fig. 1 His's diagram showing the formation of the portal vein, V.p. V.u. and 

 Y.u.d., parts of the right umbilical vein. V.u.s., left umbilical vein. V. Ar., 

 ductus venosus. 1 



the place where the right and left vitelline veins unite is near the 

 3 r olk-sac, as shown in the reconstructions by Lewis and Thyng; 

 and this is far removed from the area included in His's figure. 



The true relations of these vessels, as here described, have 

 doubtless been w T ell understood by investigators of the venous 

 system, but it is difficult to find an explicit account of them. 

 Luschka recognized a vitelline vein coming from the yolk-sac 

 and a mesenteric vein coming from the mesentery, but apparently 

 he did not consider the possibility that the mesenteric vein might 

 be derived from a left vitelline vein. This possibility, suggested 



1 For the use of the electrotype of this figure, and for many facilities for study 

 and investigation during my stay at the Harvard Laboratory, I am deeply in- 

 debted to Professor Charles S. Minot. 



