THE LATER DEVELOPMENT OF THE CHICK 347 



after the right vein disappears, while proximally the connection 

 of the left vein with the ductus Cuvieri is lost, and this vessel 

 acquires a new connection with the intra-hepatic vessels and 

 ductus venosus. Through this pathway the veins of the 

 allantois then connect with the embryonic circulation. 



The largest venous trunk of the fowl is the inferior vena cava 

 or postcaval vein. As in other forms, this vein is in part an 



FIG. 137. Injected chick embryo of the third day, showing the arrangement 

 of the cardinal veins and the formation of the umbilical vein from capillary 

 networks. From Evans. A.C.V., Anterior cardinal vein; P.C.V., posterior 

 cardinal vein; U.V., umbilical vein. 



independent formation, and in part formed from the posterior 

 cardinal system. The first part of the vena cava appears 

 during the fourth day as a posterior outgrowth of the ductus 

 venosus, which connects with a series of venous spaces in the 

 dorsal wall of the liver, on the right side (Fig. 136). Soon this 



