40 METAMOKPHOSES OE MAN 



special set of vessels intervenes, between the young 

 animal and the coverings of the egg. The blood 

 highly charged with nutritious matter flows from these 

 envelopes toward the right side of the heart. As soon 

 as it arrives there, it is permitted to flow into the aorta 

 without passing into the lungs, by the aid of two 

 contrivances for the purpose — the foramen ovale, an 

 aperture through which the blood can flow from one 

 auricle into the other; and the ductus arteriosus, or 

 artery of communication between the great pulmonary 

 vessel and the aorta.* 



These anatomical peculiarities being only required 

 during the embryonic condition, are not found in the 

 adult. When the young mammal has been discharged 

 from the mother's uterus, the atmospheric air rushes 

 into the chest, and, dilating the lungs, causes the blood 

 to flow, toward these organs. Then the partition 

 between the two auricles is gradually completed, the 

 foramen ovale is stopped up, and the ductus arteriosus is 

 obliterated, and not unfrequently disappears altogether. 

 From this time forward the blood, in passing from one 

 side of the heart to the other, must flow through the 

 lungs, whose vessels have been permanently enlarged. 

 At the same period the blood-vessels, which, having 

 played the part of rootlets, had provided for the early 

 nutrition of the foetus, having been torn during birth, 

 become atrophied and are lost. The young animal 

 begins to feed itself, and the alimentary materials 

 are prepared and transmitted to the digestive organs, 

 by a mechanism which till now had been inactive. 



* For a detailed account of these special apparatus, the reader 

 will do well to consult the supplement to Midler's "Elements of 

 Physiology," translated by Baly. — Ed. 



