352 



COMPARATIVE ANATOMY 



posterior body-wall by the postcardinal veins. The two unite with the 

 sinus venosus by means of paired common cardinal veins or ductus 



PRECARDINAL V| 0O'>S»- AORTA| .COMMON CARDINAL V posrCARDINAL V 



l^^■ lUAC V 



SUP VESICAL A. 



HEPATIC V 



CORONARY A' 

 HEPATIC PORTAL 



DUODENAL a: 



Pig. 294. — Diagrams of the circulatory system of Amphioxus, Squalus, Necturus, 

 and Felis. Arteries black, veins stippled. The vessels are shown as if projected upon 

 the median plane. Arrows indicate the direction of flow of blood. A-D are believed 

 to represent an evolutionary series. In the mammal three aortic arches persist, viz., 

 carotid (3), aorta (4), and pulmonary (6 in part). (Redrawn after Wierstratz, Woodruff, 

 and Kingsley. Felis original.) 



Cuvieri. The vascular system of amphioxus thus resembles that of cyclos- 

 tomes and elasmobranchs. The blood however lacks hemoglobin and is 

 colorless. Blood cells are scarce. (Fig. 294, A) 



