ioo Motion of the 



In those animals in which the ventricles of the heart 

 are smooth within, and entirely without fibres or 

 muscular bands, or anything like foveae, as in almost 

 all the smaller birds, the partridge and the common 

 fowl, serpents, frogs, tortoises, and also fishes, for the 

 major part, there are no chordae tendinese, 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 here is still the same as elsewhere, as the 

 lungs are spongy, and loose, and soft, no great amount 

 of force is required to force the blood through them ; 

 fhence the right ventricle is either without the bundles 

 in question, or they are fewer and weaker, not so fleshy 

 ^or like muscles ; those of the left ventricle, however, 

 ^.re 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 not otherwise that are endowed 

 with particularly strong frames, and that have large and 

 fleshy limbs at a great distance from the heart, have 

 this central organ of greater thickness, strength, and 

 muscularity. And this is both obvious and necessary. 

 Those, on the contrary, that are of softer and more 

 slender make have the heart more flaccid, softer, and 

 internally either sparely or not at all fibrous. Con- 

 sider farther the use of the several valves, which are all 

 so arranged, that the blood once received into the 

 ventricles of the heart shall never regurgitate, once 

 forced into the pulmonary artery and aorta shall not 

 flow back upon the ventricles. When the valves are 

 raised and brought together they form a three-cornered 



