70 ^ lii. 4. 



which is the origin of other vessels ; inasmuch, moreover, as these 

 two vessels present differences, hereafter to be discussed, when" 

 compared with each other, it is of advantage that they also shall 

 themselves have distinct origins. This advantage will be obtained 

 if each side have its own blood, and the blood of one side be 

 kept separate from that of the other.^^ For this reason the heart, 

 whenever it is possible, has two receptacles. And this possibility- 

 exists in the case of large animals, for in them the heart, as the 

 body generally, is of large size. Again it is still better that there 

 shall be three cavities, so that the middle and odd one may serve 

 as a common origin for both sides.^^ But this requires the heart 

 to be of greater magnitude, so that it is only in the largest animals 

 that the heart has three cavities. 



Of these three cavities it is the right which has the most 

 abundant and the hottest blood,^''' and this explains why the limbs 

 on the right side of the body are also warmer than those on the 

 left.2^ The left cavity has the least blood of all, and the coldest ; 

 while in the middle cavity the blood, as regards quantity and 

 heat, is intermediate to the other two, being however of purer 

 quality than either. For it behoves the supreme part to be as 

 tranquil as possible, and this tranquillity can be ensured by the 

 blood being pure, and of moderate amount and warmth.^^ 



In the heart of animals there is also a kind of joint-like division, 

 something like the sutures of the skull.^" This is not however 

 attributable to the heart being formed by the union of several 

 parts into a compound whole, but is rather, as already said, the 

 result of a joint-like division. These jointings are most distinct 

 in animals of keen sensibility, and less so in those that are of 

 duller feeling, in swine for instance. Different hearts differ also 

 from each other in their sizes, and in their degrees of firmness ; 

 and these differences somehow extend their influence to the 

 temperaments of the animals. For in animals of low sensibility 

 the heart is hard and solid, while it is softer in such as are 

 endowed with keener feeling. So also when the heart is of large 

 size the animal is timorous, while it is more courageous if the 

 organ be smaller and of moderate bulk. For in the former the 

 bodily affection which results from terror already pre-exists ; ^^ for 

 the bulk of the heart is out of all proportion to the animal's heat, 

 which being small is reduced to insignificance in the large space, 

 and thus the blood is made colder than it would otherwise be. 

 667 a. 



