HEART AND BLOOD. 63 



ated at different distances from one another, and diversely in 

 different individuals ; they are connate at the sides of the veins ; 

 they are directed upwards or towards the trunks of the veins ; 

 the two for there are for the most part two together regard 

 each other, mutually touch, and are so ready to come into con- 

 tact by their edges, that if anything attempt to pass from the 

 trunks into the branches of the veins, or from the greater vessels 

 into the less, they completely prevent it ; they are farther so ar- 

 ranged, that the horns of those that succeed are opposite the mid- 

 dle of the convexity of those that precede, and so on alternately. 

 The discoverer of these valves did not rightly understand their 

 use, nor have succeeding anatomists added anything to our 

 knowledge : for their office is by no means explained when we 

 are told that it is to hinder the blood, by its weight, from all 

 flowing into inferior parts ; for the edges of the valves in the 

 jugular veins hang downwards, and are so contrived that they 

 prevent the blood from rising upwards ; the valves, in a word, 

 do not invariably look upwards, but always towards the trunks 

 of the veins, invariably towards the seat of the heart. I, and 

 indeed others, have sometimes found valves in the emulgent 

 veins, and in those of the mesentery, the edges of which were 

 directed towards the vena cava and vena portse. Let it be added 

 that there are no valves in the arteries [save at their roots], 

 and that dogs, oxen, &c., have invariably valves at the divisions 

 of their crural veins, in the veins that meet towards the top of 

 the os sacrum, and in those branches which come from the 

 haunches, in which no such effect of gravity from the erect 

 position was to be apprehended. Neither are there valves in the 

 jugular veins for the purpose of guarding against apoplexy, as 

 some have said ; because in sleep the head is more apt to be 

 influenced by the contents of the carotid arteries. Neither are 

 the valves present, in order that the blood may be retained in 

 the divarications or smaller trunks and minuter branches, and 

 not be suffered to flow entirely into the more open and capa- 

 cious channels ; for they occur where there are no divarica- 

 tions ; 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 disposed to flow with sufficient slowness of its own accord, 



