VASCULAR SYSTEM. 127 



^. The black blood side of the heart; and the reason is 

 that the circulation ordinarily stops first in the lungs, and 

 the blood is by this pulmonary obstruction, collected in 

 the right side of the heart. 



Q. Why is there weakness of parietes, slowness of mo- 

 tion, and great capacity in the veins? 



#. The parietes are comparatively weak, because the 

 veins have little impulse to support; the velocity is not so 

 great as in the arteries, because the force of the heart is so 

 little felt in the veins ; the capacity is great in the veins 

 that they may bear accumulations from gravity and other 

 causes with safety. 



Q. What is the result of a diminution of the velocity 

 of the blood in the veins? 



#. It increases the capacity of the veins; hence the dif- 

 ference in the capacity of the veins of the inferior and su- 

 perior extremities. 



Q. What is the principal point of difference in the 

 branches of the veins and arteries? 



#. The venous are much less tortuous, and hence there 

 is no locomotion in them. 



Q. Where are the ramifications and small branches 

 of the veins usually found? 



Jl. The ramifications form a constituent part of the in- 

 terior of an organ: the branches lie in the interstices, 

 lobes and circumvolutions of the organs. 



Q. Why are the large arterial and venous trunks deep- 

 seated ? 



<fl. To preserve them from injury. 



Q. Considering the venous system as a whole, what 

 three trunks compose it? 



