AN ANATOMICAL STUDY ON THE 



This canal gradually shrinks after birth and is 

 finally obliterated like the umbilical vessels. 



There is no membrane in this arterial canal to 

 impede the movement of the blood in either direction. 

 At the entrance of the pulmonary artery, from which 

 this canal extends, there are three sigmoid valves 

 opening outwards, so the blood flows easily from the 

 right ventricle into this vessel and the aorta, but 

 by closing tightly they prevent any back flow from 

 the arteries or lungs into the right ventricle. Thus 

 when the heart contracts in the embryo, there is 

 reason to believe the blood is continually propelled 

 through this way from the right ventricle to the aorta. 



It is commonly said that these two great junctions 

 are for the nourishing of the lungs. This is improbable 

 and inconsistent, since they are closed up and 

 obliterated in the adult, although the lungs then, 

 because of their heat and motion, must be thought to 

 require more nourishment. It is also false to claim 

 that Nature had to make these passages to nourish the 

 lungs because the heart does not beat nor move in the 

 embryo. Nature feels no such need, for in the hatch- 

 ing egg, and in the human embryo, removed quickly 

 from the uterus at an autopsy, the heart beats just 

 as in an adult. I am not alone in often seeing these 

 movements, for Aristotle testifies {Lib. de Spir.y cap. 

 j)y "Being part of the constitution of the heart, the 

 pulse appears at its very beginning, as may be seen in 

 animal experiments, and in the formation of the chick.** 

 These passages are not only open to the time of 



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