356 



COMPARATIVE ANATOMY 



side of the body. Thus the right aortic arch comes from the left ventricle 

 and conveys pure blood to the dorsal aorta and the head. The left aortic 

 arch comes from the right ventricle and carries mixed blood into the 

 dorsal aorta. Consequently, the dorsal aorta of reptiles contains mixed, 



P^CATOINAL 



EXT CABCTTID A. 



■JUGULAR « 



■mjNC.AKT. 



Fig. 297. — Diagrams of the circulatory system in fish, urodele, anuran, reptile, and 

 mammal. Arteries black, veins stippled. In general features the series is believed to 

 represent stages in the phylogenesis of the mammalian circulatory system. It will be 

 noted that some blood vessels persist throughout the entire series. (Redrawn after 

 Stempell.) 



and not pure, blood. Since both celiac and mesenteric arteries are given 

 off from the left aortic arch which carries mixed blood, they carry mixed 

 blood to the stomach and intestine. In some reptiles a foramen Panissae 

 connects the blood streams in the two ventral aortae so that some mixing 

 of the blood in the two vessels may take place. In the lower reptiles 



