Development of the Third Day 201 



and 76, VD)\ this transverse vein is called the 

 ductus Cuvieri, or Cuvierian vein. 



In order to understand fully the evolution 

 of the complex avian circulation from the 

 simple and fish-like circulation of the embry- 

 onic chick, it is important that each stage in 

 the development should be clearly understood. 

 A brief description of the course of the circu- 



& 



m 



V 



FIG. 66. DIAGRAM OF THE VENOUS CIRCULA- 

 TION OF THE THIRD DAY. (After Foster and Bal- 

 four,) 



//, heart. J, jugular or anterior cardinal vein, c, inferior 

 or posterior cardinal vein. Of, vitelline vein, dc^ ductus 

 Cuvieri. 



lation of the blood at this period will, there- 

 fore, be given. 



The blood, on entering the heart, is forced, 

 by the contraction of its walls, through this 

 much-twisted but, as yet, undivided tube, to 

 the bulbus arteriosus ; from the bulbus it 

 passes dorsalward, around each side of the 

 pharynx, through the three pairs of aortic 

 arches to the two dorsal aortae which lie 



