SYSTEMATIC SYNTHESIS OF TISSUES INTO ORGANS. 319 



tending the vein. If the finger is carried below the valve, the blood is 

 pressed away from it, and the vein between the valve and finger will be 

 empty. 



Fig. 207 represents, a, vein, laid 

 open by a section of one side, show- 

 ing two sets of valves, in pairs, b, 

 same vein, in perpendicular section, 

 through one set of valves. c t same 

 vein, entire, showing the distension 

 of the vein behind the valves. 



Figs. 208, 209, 

 are plans of veins, 

 showing how the 

 blood flows into 

 side branches be- 

 low the valves when 

 they are closed. 



899. THE USE OF THE VALVES is to prevent the 

 Blood, when pressure is made upon the veins, from flow- 

 ing back into the capillaries. 



900. Remark. The valves of the lower extremities are very nu- 

 merous, yet the severe and continued pressure upon the veins there not 

 unfrequently distends them till the valves fail to close them, and the 

 Blood flows back, distending the veins below to a greater degree, caus- 

 ing a knotted appearance of the veins, called varicose. In this case, as 

 far as possible, the pressure should be removed, and an elastic bandage 

 worn over the entire extremity below the upper part of the varicose 

 condition. Standing positions are apt to produce this condition. 



901. Inf. The arrangement of the valves teaches that when the 



Describe Fig. 207. Describe Fig. 208. Describe Fig. 209. 899. What is ? 

 900. What are varicose veins ? 901. What do the valves teach ? 



