THE HUMAN BODY. 



The vascular system is completely closed except at two 

 points in the neck where lymph- vessels open into the veins; 

 there some lymph is poured in and mixed directly \^th the 

 blood. Accordingly everything which leaves. the blood must- 

 do so by ooiing through the walls of the blood-vessels, and 

 everything which enters it. must do the same, except matters 



mdu 



del 



mvs 



mvp 



imv 



FIG. 88. The arteries of the hand, showing the communications or anastomose, 

 of different arteries and the fine terminal twigs given off from the larger trunks; 

 these twigs end in the capillaries which would only become visible if magnified, .ff, 

 the radial artery on which the pulse is usually felt at the wrist ; U, the ulnar ar- 

 tery. 



conveyed in by the lymph at the points above mentioned. 

 This interchange through the walls of the vessels takes place 

 only in the capillaries, which form a sort of irrigation systerh 

 all through the Body. The heart, arteries, and veins are all' 

 merely arrangements for keeping the capillaries full and 

 renewing the blood within them. It is in the capillaries 

 alone that the blood does its ulivsiological workv 



