THE VEINS 27 



muscles of the side and back of the body, 

 and of the head as far forwards as the nose. 



b. The left anterior vena cava corresponds in its course 

 and branches to the right one. 



C. The posterior vena cava is a median vein which, com- 

 mencing between the kidneys, runs forward, dorsally 

 to the liver, to open into the posterior end of the 

 sinus venosus. It returns to the heart the blood from 

 the liver and from the kidneys, and indirectly from 

 other viscera and from the hind limbs. It receives 

 the following veins : 



i. The right and left hepatic veins, from the liver : 

 these open into the posterior vena cava just before 

 it joins the sinus venosus. 



ii. The renal veins, from the kidneys : of these there 

 are four or five on each side, which open into, or 

 rather form by their union, the posterior vena 

 cava. The most anterior of these receive the 

 veins from the fat bodies. 



iii. The ovarian veins (in the female), or spermatic 

 veins (in the male) ; returning blood from the 

 ovaries or testes. They are usually four or five 

 in number on each side, and open into the pos- 

 terior vena cava between the renal veins. 



II. Vein opening into the Left Auricle. 



a. The pulmonary vein is formed by the union of the 

 right and left pulmonary veins, returning to the 

 heart the blood from the right and left lungs respec- 

 tively. Each pulmonary vein runs along the inner 

 side of its lung. 



III. The Portal Systems. 



A portal vein is one which, returning blood from the capil- 

 laries of some part, breaks up before reaching the heart into a 

 second set of capillaries within some other organ ; these again 

 unite to form a vein which carries the blood to the heart. In 

 the frog there are two portal systems, one supplying the 

 kidneys, and the other the liver. 



