THE LATER DEVELOPMENT OF THE CHICK 345 



or lateral vitelline veins anastomose, at about the age of three 

 days, on the dorsal side of the intestine, posterior to the pan- 

 creatic rudiment (Fig. 136). Thereupon the base of the left 



ul 



FIG. 136. Diagrams illustrating the formation of the omphalomesenteric 

 and umbilical veins, in the chick. After Hochstetter. A. At about fifty-eight 

 hours. B. At about sixty-five hours. Veins joined dorsal to the gut. C. 

 At about seventy-five hours. Veins again separate. D. At about eighty hours. 

 Secondary union of veins around the gut. E. At about one hundred hours. 

 Definitive arrangement of the vessels, c. Vena cava posterior (inferior) ; dC, 

 ductus Cuvieri; dv, ductus venosus; g, gut; hi, left hepatic vein; hr, right hepatic 

 vein; Z, liver; o, omphalo-mesenteric vein; p, anterior intestinal portal ; pa, rudi- 

 ment of pancreas; ul, left umbilical vein; ur, right umbilical vein; v, vitelline 

 vein; I, II, primary and secondary venous rings around the gut. 



vein rapidly disappears, so that during the fourth day all of 

 the blood from the yolk-sac is returned to the heart by the right 

 vein, for it will be recalled that the original or anterior vitelline 

 veins have previously fused and connected with the right 



