Motion of the 



fleshy heart, in order that the nutritive fluid may be 

 propelled with yet greater force and celerity. And 

 further, inasmuch as the more perfect animals require a 

 still more perfect nutrition, and a larger supply of 

 native heat, in order that the aliment may be thoroughly 

 concocted and acquire the last degree of perfection, 

 they required both lungs and a second ventricle, which 

 should force the nutritive fluid through them. 



Every animal that has lungs has therefore two 

 ventricles to its heart, one right, another left ; and 

 wherever there is a right, there also is there a left 

 ventricle ; but the contrary of this does not hold good : 

 where there is a left there is not always a right ventricle. 

 The left ventricle I call that which is distinct in office, 

 not in place from the other, that one namely which 

 distributes the blood to the body at large, not to the 

 lungs only. Hence the left ventricle seems to form 

 the principal part of the heart ; situated in the middle, 

 more strongly marked, and constructed with greater 

 care, the heart seems formed for the sake of the left 

 ventricle, and the right but to minister to it ; for the 

 right neither reaches to the apex of the heart, nor is it 

 nearly of such strength, being three times thinner in its 

 walls, and in some sort jointed on to the left, (as 

 Aristotle says ;) though indeed it is of greater capacity, 

 inasmuch as it has not only to supply material to the 

 left ventricle, but likewise to furnish aliment to the lungs. 



It is to be observed, however, that all this is other- 

 wise in the embryo, where there is not such a difference 

 between the two ventricles ; but as in a double nut, 

 they are nearly equal in all respects, the apex of the 

 right reaching to the apex of the left, so that the heart 

 presents itself as a sort of double-pointed cone. And 

 this is so, because in the foetus, as already said, whilst 

 the blood is not passing through the lungs from the 

 right to the left cavities of the heart, but flowing by 

 the foramen ovale and ductus arteriosus, directly from, 

 the vena cava into the aorta, whence it is distributed to 



