8o Motion of the 



divarications ; although it must be owned that they 

 are most frequent at the points where branches join. 

 Neither do they exist for the purpose of rendering 

 the current of blood more slow from the centre of the 

 body ; for it seems likely that the blood would be dis- 

 posed to flow with sufficient slowness of its own accord, 

 as it would have to pass from larger into continually 

 smaller vessels, being separated from the mass and 

 fountain head, and attaining from warmer into colder 

 places. 



]But the valves are solely made and instituted lest the 

 blood should pass from the greater into the lesser veins, 

 and either rupture them or cause them to become 

 varicose ; lest, instead of advancing from the extreme 

 to the central parts of the body, the blood should 

 rather proceed along the veins from the centre to the 

 extremities ; but the delicate valves, while they readily 

 open in the right direction, entirely prevent all such 

 contrary motion, being so situated and arranged, that 

 if anything escapes, or is less perfectly obstructed by 

 the cornua of the one above, the fluid passing, as it 

 were, by the chinks between the cornua, it is imme- 

 diately received on the convexity of the one beneath, 

 which is placed transversely with reference to the 

 former, and so is effectually hindered from getting any 

 farther. 



And this I have frequently experienced in my dis- 

 sections of the veins : if I attempted to pass a probe 

 from the trunk of the veins into one of the smaller 

 branches, whatever care I took I found it impossible 

 to introduce it far any way, by reason of the valves ; 

 whilst, on the contrary, it was most easy to push it 

 along in the opposite direction, from without inwards, 

 or from the branches towards the trunks and roots. 

 In many places two valves are so placed and fitted, 

 that when raised they come exactly together in the 

 middle of the vein, and are there united by the contact 

 of their margins; and so accurate is the adaptation, 



