128 VASCULAR SYSTEM. 



tf. The cava superior, the cava inferior, and the coro- 

 nary vein. 



Q. What difference is there between the communica- 4 

 tions of the arteries and of the veins? 



/?. The venous are much more numerous than the ar- 

 terial; the first form reticular anastomoses, such as are not 

 seen in the latter. 



Q. How do you explain the continuance of the venous 

 circulation, when the sub-cutaneous veins are tied or other- 

 wise obstructed ? 



#. The free communications between the superficial 

 and deep-seated veins account for it. 



Q. Name one great distinctive mark between the red 

 and black blood circulation? 



t/?. The influence of gravity in the venous circulation. 

 Q. What arrangement is particularly destined to coun- 

 teract this gravity ? 



.#. The valves of the veins. 

 Q. Why is gravity so powerful in the veins? 

 . Because there is no agent of impulse at the origin 

 of the black blood circulation in the general capillary sys- 

 tem. 



Q. What is the office of the vena azygos ? 

 /?. To anastomose between the superior and inferior 

 cava. This free anastomosis precludes the idea of hepatic 

 pressure on the cava producing dropsy; the blood finding 

 its way through the azygos. 



