96 THE ANATOMY OF VEETEBRATED ANIMALS. 



coalescence of the efferent veins of the kidneys and re- 

 productive organs, and does not always receive the whole 

 of the hepatic veins — more or fewer of the latter opening 

 indei^eudently into the sinus venosus. 



The blood which leaves the kidneys by its efferent veins 

 is supplied, not only by the renal arteries, but by the veins 

 of the caudal region, and of the hinder extremities, which 

 branch out like a vena portoe. in the substance of the 

 kidneys. This renal portal system is less developed in 

 Reptilia than in Amphibia. All the blood of the posterior 

 extremities and caudal region does not traverse the kidneys, 

 however, more or less of it being led away by great branches 

 of the iliac veins, which run along the anterior wall of the 

 abdominal cavity, either as two trunks, or united into one. 

 These vence abdominales anteriores are eventually distri- 

 buted to the liver, along with the branches of the proper 

 vence poi-toe. 



In Birds, the sinus venosus is not distinct from the right 

 auricle, and there are two anterior vence cavce. The vena 

 cava inferior arises, as in Mammals, by the union of the 

 two common iliac veins. It receives both the right and 

 the left hepatic veins, and, in addition, the anterior abdo- 

 minal vein no longer enters the portal system, but passes 

 up the anterior wall of the abdomen and through the 

 hepatic fissure to join the inferior cava. 



The caudal and pelvic veins unite into three principal 

 trunks, of which one is median and two are lateral. The 

 median enters into the portal system. The lateral branches 

 pass along and through the kidney, receiving veins from 

 it, biit giving none to it ; and eventually, after receiving the 

 ischiatic veins, unite with the crural veins to form the com- 

 mon iliacs. Thus there is no renal portal system in birds. 



In Mammalia, the simis venosus is not distinct from the 

 right auricle. The anterior cavce are frequently reduced to 

 one, the right. The vena cava inferior commences in the 

 caudal region, and receives all the blood of the j)osterior 

 moiety of the body, except so much as is can-ied away by 

 the azygous veins. The anterior abdominal veins are repre- 



