MOTION OF THE HEART AND BLOOD 



for they are placed where there are no branches 

 at all, although I confess they are more frequently 

 seen where there are branchings. Nor are they 

 present for slowing the flow of blood from the center 

 of the body, for it seems likely it would flow slowly 

 enough anyway, as it would then be passed from 

 larger to smaller branches, become separated from 

 the source and mass, and be moved from warmer 

 to cooler places. 



The valves are present solely that blood may 

 not move from the larger veins into the smaller ones 

 lest it rupture or varicose them, and that it may 

 not advance from the center of the body into the 

 periphery through them, but rather from the 

 extremities to the center. This latter movement 

 is facilitated by these delicate valves, the contrary 

 completely prevented. They are so situated that 

 what may pass the horns of a set above is checked 

 by those below, for whatever may slip past the 

 edges of one set is caught on the convexity of those 

 beyond, so it may not pass farther. 



I have often noticed in dissecting veins, that no 

 matter how much care I take, it is impossible to 

 pass a probe from the main venous trunks very 

 far into the smaller branches on account of the 

 valvular obstructions. On the contrary it is very 

 easy to push it in the opposite direction, from the 

 branches toward the larger trunks. In many places 

 a pair of valves are so placed that when raised they 

 join in the middle of the vein, and their edges are 



I99] 



