AN ANATOMICAL STUDY ON THE 



so nicely united that one cannot perceive any 

 crack along their junction. On the other hand, 

 they yield to a probe introduced from without 

 inwards and are easily released in the manner of 

 flood-gates opposing a river flow. So they inter- 

 cept, and when tightly closed, completely prevent 

 in many places a flow of blood back from the heart 

 and vena cava. They are so constituted that they 

 can never permit blood to move in the veins from 

 the heart upwards to the head, downwards toward 

 the feet, or sidewise to the arms. They oppose any 

 movement of blood from the larger veins toward 

 the smaller ones, but they favor and facilitate 

 a free and open route starting from the small veins 

 and ending in the larger ones. 



This fact may be more clearly shown by tying off 

 an arm of a subject as if for blood-letting (^, yf, 

 fig. i). There will appear at intervals (especially 

 in rustics) knots, or swellings, like nodules (B, C, 

 D, Ey F), not only where there is branching (£, F), 

 but also where none occurs (C, D), These are caused 

 by the valves, appearing thus on the surface of the 

 hand and arm. If you will clear the blood away from 

 a nodule or valve by pressing a thumb or finger 

 below it (//, fig. 2), you will see that nothing can 

 flow back, being entirely prevented by the valve, 

 and that the part of the vein between the swelling 

 and the finger (i7, 0, fig. 2), disappears, while 

 above the swelling or valve it is well distended 

 (0, G). Keeping the vein thus empty of blood, if 



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