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THE HUMAN BODY 



The Valves of the Veins. Except the pulmonary artery 

 and the aorta, which have the semilunar valves, arteries have 

 no valves. Most veins, on the contrary, contain many valves 

 formed by pouches of their lining, which resemble in form 

 the semilunar valves of the aorta and the pulmonary artery, 



FIG. 61. A small portion of the capillary network as seen in the frog's web when 

 magnified about 23 d'ameters. a, a small artery feeding the capillaries; v, v, small 

 veins carrying blood back from the latter. 



What arteries have valves? Where are these valves placed? 

 How do veins differ from arteries in regard to the presence of valves 

 in them? 



