700 



MANUAL OF PHYSIOLOGY. 



into two, which differ in their time of appearance and in the ac- 

 cessory organs to which they are distributed. Though they may, 

 for the sake of clearness, be described as two independent circu- 



ILOJU 



Diagram of the circulation of a chick at the end of the third day. (Foster 

 and Bal four )H. Heart. AA. Aortic arches (2d, 3d, and 4th). A o. Dor- 

 sal aorta. L.ofA., R.ofA. Right and left omphalo-mesenteric arteries. 

 S.T. Sinus tertninalis. R.of, and L.of. Right and left omphalo-mesenteric 

 veins. S. V. Sinus venosus. D.C. Duct of Cuvier. S. Ca. and V.Ca. Supe- 

 rior and inferior cardinal veins. 



lations, they are not strictly so, as they exist for a short time 

 coincidently, and arise in connection with one another from the 

 same heart. 



(a) The earlier or vitelline circulation is that which is directed 



