CIRCULATION OF THE BLOOD 14> 



from the aorta. And the same proportion in these particulars 

 is universally preserved. The more muscular and powerful 

 men are, the firmer their flesh ; the stronger, thicker, denser, 

 and more fibrous their hearts, the thicker, closer, and stronger 

 are the auricles and arteries. Again, in those animals the 

 ventricles of whose hearts are smooth on their inner surface, 

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

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

 the arteries differ little or nothing in the thickness of their 

 coats from the veins. 



Moreover, the reason why the lungs have such ample 

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

 pulmonary veins exceeds that of both crural and jugular ves- 

 sels), 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 pulmonary vein and 

 left ventricle so full of blood, of the same black colour and 

 clotted character as that with which the right ventricle and 

 pulmonary artery are filled, is because the blood is incessantly 

 passing from one side of the heart to the other through the 

 lungs. Wherefore, in fine, the pulmonary artery has the 

 structure of an artery, and the pulmonary veins have the 

 structure of veins. In function and constitution and every- 

 thing else the first is an artery, the others are veins, contrary 

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

 monary artery has so large an orifice is because it trans- 

 ports 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 and fully to confirm the truth contended for 

 throughout these pages, and at the same time to oppose the 

 vulgar opinion; for it would be very difficult td explain in 

 any other way to what purpose all is constructed and ar- 

 ranged as we have seen it to be. 



