454 MAMMALIA— PHYSIOLOGY 



is a quite definite correlation between longevity and the rapidity 

 of the pulse. (See tables, pages 496 and 498.) 



Portal Circulation. — The blood which comes to the spleen, 

 stomach and intestines passes first through the capillaries of these 

 organs and then by their veins into one, the portal vein, which goes 

 to the liver and there breaks up into capillaries, then passes from 

 the liver into the post cava. The wastes are conveyed from the 

 liver by way of the bile duct which leads into the digestive tube. 

 But bile acids and salts are extremely important. 



The Comparative Anatomy of the Portal Systems. — In a portal 

 system the blood is collected in capillaries, passes through a vein to 

 an organ of purification, thence by capillaries to another vein that 

 brings the purified blood into the heart. 



(i) The hepatic portal system consists of the union of veins from 

 the stomach, intestine, spleen and pancreas, which passes into 

 the liver as the hepatic portal vein, then breaks up into capillaries, 

 its blood mingling with the blood brought into the liver by the 

 hepatic artery. Capillaries in the liver unite to form the hepatic 

 veins which send the purified blood into the sinus venosus. The 

 hepatic portal system persists throughout the vertebrates. 



(2) The rey^al portal system arises in the Elasmobranchii and 

 almost completely disappears in the Aves. 



Elasmobranchii. The caudal divides into right and left portal veins which pass to the 

 kidneys. The course thence is to the cardinal veins. 



Teleostii. The caudal divides into two branches, of which the right continues 



into the corresponding cardinal and the left breaks up in the kid- 

 ney. 



Amphibia. Salamander. 



The caudal divides into two renal portal veins. The efferent renal 



veins form the postcaval. 

 Frog. 



The femorals each divide into a dorsal and a ventral branch. The 

 ventral branch, the pelvic vein, unites with its fellow to form the 

 abdominal vein. The dorsal branch becomes the renal portal, 

 receives the sciatic and passes to the kidney. 



Reptilia. The turtle has no renal portal system. In the lizard the caudal 



divides into two pelvics which become the renal portals. As in 

 the salamanders, the efferent renal veins unite to aid in forming 

 the postcaval. 



