Heart and Blood 45 



nate in the arteria magna or aorta. In the embryo, 

 consequently, there are, as it were, two aortas, or two 

 roots of the arteria magna, springing from the heart. 

 This canalis arteriosus shrinks gradually after birth, 

 and is at length and finally almost entirely withered, 

 and removed, like the umbilical vessels. 



The canalis arteriosus contains no membrane or 

 valve to direct or impede the flow of the blood in this 

 or in that direction : for at the root of the vena 

 arteriosa, or pulmonary artery, of which the canalis 

 arteriosus is the continuation in the foetus, there are 

 three sigmoid or semilunar valves, which open from 

 within outwards, and oppose no obstacle to the blood 

 flowing in this direction or from the right ventricle into 

 the pulmonary artery and aorta ; but they prevent all 

 regurgitation from the aorta or pulmonic vessels back 

 upon the right ventricle ; closing with perfect accuracy, 

 they oppose an effectual obstacle to everything of the 

 kind in the embryo. So that there is also reason to 

 believe that when the heart contracts, the blood is 

 regularly propelled by the canal or passage indicated 

 from the right ventricle into the aorta. 



What is commonly said in regard to these two great 

 communications, to wit, that they exist for the nutrition 

 of the lungs is both improbable and inconsistent ; 

 seeing that in the adult they are closed up, abolished, 

 and consolidated, although the lungs, by reason of their 

 heat and motion, must then be presumed to require 

 a larger supply of nourishment. The same may be said 

 in regard to the assertion that the heart in the embryo 

 does not pulsate, that it neither acts nor moves, so 

 that nature was forced to make these communications 

 for the nutrition of the lungs. This is plainly false ; 

 for simple inspection of the incubated egg, and of 

 embryos just taken out of the uterus, shows that the 

 heart moves precisely in them as in adults, and that 

 nature feels no such necessity. I have myself re- 

 peatedly seen these motions, and Aristotle is likewise 



