66 THEPHILOSOPHY 



peds ; and Nature has accompllfhed this purpofe by a very fimple 

 artifice. 



In man, and in all land-quadrupeds, the lungs of the foetus have 

 no motion, and receive no more blood than is requifite for their 

 growth and nourlfhment. But, immediately after birth, the young 

 animals refpire, and the vphole mafs of blood circulates through 

 their lungs. To carry on the circulation in the foetus ftate, another 

 paflage was neceflary. The blood in the right auricle of the heart, 

 inftead of paffing into the pulmonary artery, and, after circulating 

 through the lungs, returning into the left auricle by the pulmonary 

 vein, pafles diredly from the right to the left auricle through aa 

 aperture called \heforameti o'uale, which is fituated in the partition 

 of the heart that feparates the cavities of the two auricles. By this 

 contrivance, the mafs of blood, without deviating into the lungs, 

 enters the aorta, and is diftributed over every part of the body.. In 

 man, and the other terreftrial animals, the foramen ovale of the heart,, 

 which permits the foetus to live without refpiration, clofes the mo- 

 ment after birth, and remains fhut during life. Animals of this 

 conftrudion can neither live without air, nor remain long under 

 water, without being fuffocated. 



But, in the feal, walrus, and other amphibious animals, the fora- 

 men ovale continues open during life, though the mothers bring 

 forth on land, and refpiration commences immediately after birth. 

 By means of this perpetual aperture in the feptum or partition of 

 the heart, which allows a dired; communication of the blood from 

 the vena cava to the aorta, thefe animals enjoy the privilege of re- 

 fpiring, or not, at their pleafure. 



This fingularity in the ftrudure of the heart, and the confequent 

 capacity of living equally on land and in water, mull neceflarily 



produce 



