CIRCULATION OF THE BLOOD 83 



tense, but in the systole, for then only, when tense, is it 

 moved and made vigorous. 



Neither is it by any means to be allowed that the heart 

 only moves in the lines of its straight fibres, although the 

 great Vesalius giving this notion countenance, quotes a 

 bundle of osiers bound in a pyramidal heap in illustration; 

 meaning, that as the apex is approached to the base, so are 

 the sides made to bulge out in the fashion of arches, the 

 cavities to dilate, the ventricles to acquire the form of a 

 cupping-glass and so to suck in the blood. But the true effect 

 of every one of its fibres is to constringe the heart at the 

 same time they render it tense; and this rather with the 

 effect of thickening and amplifying the walls and substance 

 of the organ than enlarging its ventricles. And, again, as 

 the fibres run from the apex to the base, and draw the 

 apex towards the base, they do not tend to make the walls 

 of the heart bulge out in circles, but rather the contrary; 

 inasmuch as every fibre that is circularly disposed, tends to 

 become straight when it contracts ; and is distended laterally 

 and thickened, as in the case of muscular fibres in general, 

 when they contract, that is, when they are shortened longi- 

 tudinally, as we see them in the bellies of the muscles of 

 the body at large. To all this let it be added, that not only 

 are the ventricles contracted in virtue of the direction and 

 condensation of their walls, but farther, that those fibres, 

 or bands, styled nerves by Aristotle, which are so conspicu- 

 ous in the ventricles of the larger animals, and contain all 

 the straight fibres (the parietes of the heart containing only 

 circular ones), when they contract simultaneously by an 

 admirable adjustment all the internal surfaces are drawn 

 together as if with cords, and so is the charge of blood 

 expelled with force. 



Neither is it true, as vulgarly believed, that the heart by 

 any dilatation or motion of its own, has the power of draw- 

 ing the blood into the ventricles; for when it acts and be- 

 comes tense, the blood is expelled ; when it relaxes and sinks 

 together it receives the blood in the manner and wise which 

 will by-and-by be explained. 



