ANIMAL BIOLOGY. [Parti. 



8. But when the kidneys are developing, the blood from them 

 and from the hind limbs is led by a new median vein, the post- 

 caval (pL c.), into the sinus venosus. 



9. As the postcaval increases in size the posterior cardinals 

 diminish and tend to atrophy. 



Fia. 66.- DIAGRAM OF VENOUS CIRCULATION OF CHICK PREVIOUS TO HATCHING. 



a. c. Anterior cardinal vein, the jugular of the adult, al. c. Alimentary 

 canal, al. v. Allantoic vein. als. Allantois ; this and its vein are provi- 

 sional embryonic structures. Ir. Brachial vein. cr. Crural vein. d. c. 

 Ductus Cuvieri, the precaval of the adult, d. i: Ductus venosus, leading 

 blood through the liver ; atrophies in the adult, h. Heart, lie. Hepatic 

 vein, collecting blood from the liver, fc. Kidney. Ir. Liver, m. v. Mesen- 

 teric vein. p. c. Posterior cardinal vein, bringing blood from the Wolffian 

 bodies, atrophies in the adult, p. v. Portal vein, delivering some blood to 

 the substance of the liver, but delivering more through the ductus venosus 

 to the sinus venosus. pt. c. Postcaval vein. r. Renal vein. s. v. Sinus 

 venosus. v. v. Vitelline vein. w. 6. Wolffian bodies, atrophy with the 

 growth of the kidneys, yk. s. Yolk-sac, which, with its vitelline vein, are 

 provisional embryonic structures. 



All details diagrammatic : relative size of parts not indicated. 



10. With the atrophy of the posterior cardinals the ductus 

 Cuvieri become the precavals, which also receive factors from the 

 wing and breast. 



11. During foetal life there is a communication between the 

 two auricles by the foramen ovale, through which the arrow 



