140 WILLIAM HARVEY 



superadded and supplementary to the heart, assisting it to 

 execute a more powerful and perfect contraction, and so 

 proving subservient to the complete expulsion of the blood. 

 They are, in some sort, like the elaborate and artful arrange- 

 ment of ropes in a ship, bracing the heart on every side as 

 it contracts, and so enabling it more effectually and forcibly 

 to expel the charge of blood from its ventricles. This much 

 is plain, at all events, that in some animals they are less 

 strongly marked than in others; and, in all that have them, 

 they are more numerous and stronger in the left than in 

 the right ventricle ; and while some have them present in 

 the left, yet they are absent in the right ventricle. In man 

 they are more numerous in the left than in the right ventri- 

 cle, more abundant in the ventricles than in the auricles ; and 

 occasionally there appear to be none present in the auricles. 

 They are numerous in the large, more muscular and hardier 

 bodies of countrymen, but fewer in more slender frames and 

 in females. 



In those animals in which the ventricles of the heart are 

 smooth within and entirely without fibres of muscular bands, 

 or anything like hollow pits, as in almost all the smaller birds, 

 the partridge and the common fowl, serpents, frogs, tortoises, 

 and most fishes, there are no chordae tendineae, nor bundles 

 of fibres, neither are there any tricuspid valves in the 

 ventricles. 



Some animals have the right ventricle smooth internally, 

 but the left provided with fibrous bands, such as the goose, 

 swan, and larger birds ; and the reason is the same here as 

 elsewhere. As the lungs are spongy and loose and soft, no 

 great amount of force is required to force the blood through 

 them; therefore the right ventricle is either without the 

 bundles in question, or they are fewer and weaker, and not 

 so fleshy or like muscles. Those of the left ventricle, how- 

 ever, are both stronger and more numerous, more fleshy and 

 muscular, because the left ventricle requires to be stronger, 

 inasmuch as the blood which it propels has to be driven 

 through the whole body. And this, too, is the reason why 

 the left ventricle occupies the middle of the heart, and has 

 parietes three times thicker and stronger than those of the 

 right. Hence all animals and among men it is similar 



