A,B    Action of valve in a vein (longitudinal section)
A    Valve open
B    Valve closed
C-E    Diagram showing how muscle contraction around veins flow blood towrads heart
C    Muscles relaxed, valves closed
D    Muscles contract upper valve opens lower valves closed
E    Muscle relaxed upper valve closed lower valve closed
F    Direction of blood flow
1    Valve
2    Vein
3    Muscle