PHILOSOPHICAL TRANSACTIOKS, [aNNO 1702. 



great trunk, at a far greater distance from the testes, than the arteries of any 

 other part of the body. Nor would the testes, which are such necessary organs, 

 have been thus exposed to external injuries, if the design of nature in lengthen- 

 ing their blood vessels had not been very considerable. Besides this lengthen- 

 ing of the spermatic arteries, we find nature still contriving other impediments 

 to check the current of the blood in those parts; it seems for this purpose that 

 the spermatic arteries are lessened at their original from the trunk of the arteria 

 magna in men, and that the spermatic arteries of quadrupeds are so much con- 

 torted before they reach their testes. 



The principal design of nature in these different contrivances seems to be, 

 that if the human spermatic arteries were contorted as in quadrupeds, before 

 they reach their testes, the apertures in the abdominal muscles of men must 

 have been much larger than they now are, and would frequently let the in- 

 testines descend into the scrotum; which nevertheless often happens: such 

 ruptures are not so incident to quadrupeds, though the passages for their sper- 

 matic vessels, through the abdominal muscles, are much wider than in men, 

 because the position of the trunks of their bodies is horizontal, and their in- 

 testines therefore cannot press on the processes of the peritonaeum, as in men, 

 who are erect. 



After the circulation of the blood through the heart, lungs, and large blood 

 vessels was demonstrated by Dr. Harvey, it was only guessed how the extremi- 

 ties of the arteries transmitted the blood to the veins, till Mr. Leuwenhoeck's mi- 

 croscopes had discovered the continuations of the extremities of those vessels in 

 fish, frogs, &c. Yet there are some who doubt of the like continuations of 

 the extremities of arteries and veins in human bodies and quadrupeds ; since 

 those animals it has hitherto been seen in, have been either such fish, or of the 

 amphibious kind, as have only one ventricle in their hearts, and their blood 

 actually cold, except in bats, where it appears very obscurely : besides, that the 

 blood in those animals does not circulate with such rapidity as in those whose 

 hearts have two ventricles : for in all animals that have biventrous hearts, the 

 vessels of the rest of the body return their blood to the heart in equal time and 

 quantity with those of the lungs, notwithstanding the inequality of their course. 



* This difference in the principal organs of the circulation of the blood in 



* Mr. Wotton in his Reflections upon Ancient and Modern Learning, chap, xviii. says, " Since it 

 has been constantly found that nature follows like methods in all sorts of animals, where she uses the 

 same instruments, it will always be believed, that the blood circulates in men after the same manner 

 as it does in eels, perches, bats, and some other creatures, in which Monsieur Leuwenhoeck tried it. 

 Though the ways how it may be visible to the eye in men, have not, that I know of, been yet 

 discovered."— Orig. . ■ , , , 



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