ANIMALS. 383 



thicken. Within this the embryo is still farther 

 involved in two membranes, called the chorion 

 and amnios ; and floats in a thin transparent fluid, 

 upon which it seems in some measure to subsist. 

 However, the great store-house from whence its 

 chief nourishment is supplied, is called the pla- 

 centa, a red substance, somewhat resembling a 

 sponge, that adheres to the inside of the womb, 

 and communicates, by the umbilical vessels, with 

 the embryo. These umbilical vessels, which con- 

 sist of a vein and two arteries, issue from the 

 navel of the child, and are branched out upon the 

 placenta ; where they, in fact, seem to form its 

 substance, and, if I may so express it, to suck 

 up their nourishment from the womb, and the 

 fluids contained therein. The blood thus receiv- 

 ed from the womb by the placenta, and commu- 

 nicated by the umbilical vein to the body of the 

 embryo, is conveyed to the heart ; where, with- 

 out ever passing into the lungs, as in the bom 

 infant, it takes a shorter course ; for, entering the 

 right auricle of the heart, instead of passing up 

 into the pulmonary artery, it seems to break this 

 partition, and goes directly through the body of 

 the heart, by an opening called the foramen 

 ovale, and from thence to the aorta, or great ar- 

 tery, by which it is driven into all parts of the 

 body. Thus we see the placenta, in some mea- 

 sure, supplying the place of lungs ; for, as the 

 little animal can receive no air by inspiration, the 

 lungs are therefore useless. But we see the pla- 

 centa converting the fluid of the womb into 

 blood, and sending it, by the umbilical vein, to 



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