804 



COMPARATIVE ANATOMY 



A. 



B. 



c. 



Fig. 456. 



Diagrams to show arrangement of principal veins in A, Urodele, B, Anura and 

 Reptilia, C, Bird, D, Mammal. 1, Sinus venosus, gradually disappearing in the 

 higher forms; 2, Ductus Cuvieri (superior vena cava) ; 3, Internal jugular (anterior 

 cardinal sinus or vein) ; 4, External jugular (sub-branchial) ; 5, Subclavian; 6, 

 Posterior cardinal, front part (venae azygos and hemiazygos of higher forms) ; 

 7, Inferior vena cava; 8, Renal portal (hinder part of posterior cardinal) ; 9, 

 Caudal; 10, Sciatic (internal iliac) ; 11, Femoral in A, Pelvic in B; 12, Anterior 

 abdominal in A and B, coccygeomesenteric in C; 13, Femoral (external iliac) in 

 B, C, and D; 14, Anastomosis of jugulars in C. (From Shipley and MacBride.) 



The sinus venosus receives the venous blood from two precaval 

 (really the Cuvierian duct) and one postcaval vein. The blood passes 

 through the right auricle into the right half of the ventricle, after which 

 it passes through the pulmonary arteries to the lungs. From the lungs 

 it returns through the pulmonary veins to the left auricle and thence to 

 the left ventricle. From here it is pumped out through the paired aortic 

 arches to all parts of the body. There is both a renal and a hepatic 

 portal system. 



Often there is a foramen (of Panizza) connecting the right and left 

 fourth aortic arches, so that blood can pass from one side to the other. 



BIRDS (Figs. 444, 446, 447, 448, 452) 



The heart is large and has two definite auricles, two ventricles, and 

 no distinct sinus venosus. The right auricle receives the venous blood 

 from the general body, while the left receives the aerated blood as it is 

 returned from the lungs. The right aortic arch carries all of the arterial 

 blood to the system. The renal-portal system is vestigial. 



MAMMALIA 



The mammals retain the left aortic arch and lose the right, while 

 birds retain the right arch and lose the left. Modern reptiles show a 

 tendency to reduce the left arch. 



The valves between auricle and ventricle are tricuspid on the right 



