HEART AND BLOOD. 85 



right ventricle of the heart are weaker and thinner than those 

 of the left ventricle ; and in like manner, in the same degree 

 in which the lungs are softer and laxer in structure than the 

 flesh and other constituents of the body at large, do the tunics 

 of the branches of the pulmonary artery differ from the tunics of 

 the vessels derived from the aorta. And the same proportion 

 in these several particulars is universally preserved. The more 

 muscular and powerful men are, the firmer their flesh, the 

 stronger, thicker, denser, and more fibrous their heart, in the 

 same proportion are the auricles and arteries in all respects 

 thicker, closer, and stronger. And again, and on the other hand, 

 in those animals the ventricles of whose heart are smooth within, 

 without villi or valves, and the walls of which are thinner, as in 

 fishes, serpents, birds, and very many genera of animals, in all 

 of them the arteries differ little or nothing in the thickness of 

 their coats from the veins. 



Farther, the reason why the lungs have such ample vessels, 

 both arteries and veins, (for the capacity of the pulmonary veins 

 exceeds that of both the crural and jugular vessels,) and why they 

 contain so large a quantity of blood, as by experience and ocular 

 inspection we know they do, admonished of the fact indeed by 

 Aristotle, and not led into error by the appearances found in 

 animals which have been bled to death, is, because the blood 

 has its fountain, and storehouse, and the workshop of its last 

 perfection in the heart and lungs. Why, in the same way 

 we find in the course of our anatomical dissections the arte- 

 ria venosa and left ventricle so full of blood, of the same black 

 colour and clotted character, too, as that with which the right 

 ventricle and pulmonary artery are filled, inasmuch as the 

 blood is incessantly passing from one side of the heart to the 

 other through the lungs. Wherefore, in fine, the pulmonary 

 artery or vena arteriosa has the constitution of an artery, and 

 the pulmonary veins or arterise venosse have the structure of 

 veins; because, in sooth, in function and constitution, and 

 everything else, the first is an artery, the others are veins, in 

 opposition to what is commonly believed; and why the pul- 

 monary artery has so large an orifice, because it transports 

 much more blood than is requisite for the nutrition of the lungs. 



All these appearances, and many others, to be noted in the 

 course of dissection, if rightly weighed, seem clearly to illustrate 



