542 



VEINS OF THE CHICK. 



of the Wolffian bodies. When the true kidneys are formed it also receives 

 blood from them, and thenceforward enlarging rapidly becomes the channel 



Su.V 



FIG. 371. DIAGRAM OF THE VENOUS CIECULATION IN THE CHICK AT THE COMMENCEMENT 



OF THE FIFTH DAY. 



H. heart ; DC. ductus Cuvieri. Into the ductus Cuvieri of each side fall J. the 

 jugular vein, Su.V. the superior vertebral, W. the vein from the wing, and C. the 

 inferior cardinal vein ; S. V. sinus venosus ; Of. vitelline vein ; U. allantoic vein, which 

 at this stage gives off branches to the body- walls ; V.C.I, inferior vena cava. 



by which the greater part of the blood from the hinder part of the body 

 finds its way to the heart. In proportion as the vena cava inferior in- 

 creases in size, the posterior cardinal veins diminish. 



The blood originally coming to them from the posterior part of the 

 spinal cord and trunk is transported into two posterior vertebral vein.!*, 

 similar to those in Reptilia, which are however placed dorsal ly to the heads 

 of the ribs, and join the anterior vertebral veins. "With their appearance 

 the anterior parts of the posterior cardinals disappear. The blood from 

 the hind limbs becomes transported directly through the kidney into the 

 vena cava inferior, without forming a renal portal system 1 . 



On the third day the course of the vessels from the yolk-sack is very 

 simple. The two vitelline veins, of which the right is already the smaller, 

 form the ductus venosus, from which, as it passes through the liver on its 

 way to the heart, are given off the two sets of vence advehentes and vence 

 rcvehentes (fig. 371). 



With the appearance of the allaiitois on the fourth day, a new feature 

 is introduced. From the ductus venosus there is given off a vein which 



1 The mode in which this is effected requires further investigation. 



