HEART AND BLOOD. 77 



merely agitated by an auricle as it is in lower forms. And 

 then in regard to animals that are yet larger, warmer, and more 

 perfect, as they abound in blood, which is ever hotter and more 

 spirituous, and possess bodies of greater size and consistency, 

 they require a larger, stronger, and more 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 con- 

 cocted 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 righ, 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 dis- 

 tributes 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 otherwise 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 the whole body, both ventricles have 

 in fact the same office to perform, whence their equality of 

 constitution. It is only when the lungs come to be used, and 



