PARTS OF ANIMALS, III. iv. 



the rest, and it lies towards the breast, and altogether 

 in the fore part of the body so as to prevent it from 

 getting cooled : for in all animals the breast has com- 

 paratively little flesh on it, Avhile the back is well 

 supplied and so gives the heat of the body ample 

 protection on that side. In animals other than man 

 the heart is in the centre of the region of the breast ; 

 in man it inclines slightly to the left side so as to 

 counteract the cooling there, for in man the left side 

 is much colder than in other creatures. I have 

 said already that the placing of the heart is the 

 same in fishes as in other animals, though it appears 

 to be different, together \Wth the reasons " for the 

 apparent difference. In fishes its apex is turned to- 

 wards the head * ; but in them the head is " forwards," 

 because the head is in the line of direction in which 

 they move. 



The heart has in it an abundance of sinews, Avhich 

 is reasonable enough, as the motions of the body have 

 their origin there ; and as these are performed by 

 contraction and relaxation, the heart needs the sineΛvs 

 to serve it and to give it strength. We have said 

 already that the heart is like a living creature inside 

 the body that contains it. 



In all cases that we have examined the heart is 

 boneless, except in horses and a certain kind of ox. 

 In these, oA\-ing to its great size, the heart has a bone 

 for a support, just as the whole body is supported 

 by bones. 



In the large animals, the heart has three cavities, in 

 the smaller ones, two only ; and in no species has it less 

 than one. The reason for this has been given : there 



appear to be an exception to this rule, but only because in 

 them " forwards " is towards the head. 



241 



