Chap. 42.] in tht Fat us. 40 9 



The veins of the placenta unite into a Tingle trunk, 

 which, leaving the placenta, enters the navel of the 

 foetus. Two arteries, which are continued from the 

 internal iliac arteries, pafs out at the navel of the 

 foetus and enter the placenta; and thefe, with the 

 vein above mentioned, conftitute the umbilical cord. 

 By means of thefe arteries and veins, a communication 

 is maintained between the fcetus and the placenta. 

 The umbilical veflels do not run in a direct courfe, 

 but both the arteries and the vein are mutually twifted 

 about each other. The umbilical cord paries from 

 the fcetus to the placenta, through the liquor amniL 

 The winding courfe of thefe veflels, and the elafticity 

 of the fubftance which furrounds them, protect them 

 in a great meafure from the bad effects which would 

 otherwife happen, from their being ftretched or 

 piefTed, which might put a flop to the circulation. 

 Befides thefe vefTels, however, there is another ia 

 brutes, called the urachus, which conveys the urine 

 from the bladder to a vefifel called the allantoides. 

 In the human fpecies, both the urachus and the allan- 

 toides are wanting. 



There is, indeed, in the human fcetus, fomething 

 like an urachus, which goes from the bladder of the 

 foetus to the navel, between the umbilical arteries, but 

 it feems to be of no ufe, as it does not communicate 

 with the bladder. 



The umbilical vein, after it has entered the body 

 of the foetus, divides into two branches, one of which 

 enters the vena portarum to be diftributed in the liver; 

 the other, which is called the ductus venofus, carries 

 its contents to the left vena cava hepatis, which ter- 

 minates in the great vena cava ; and that part of the 

 blood -which paries through the liver alfo arrives at the 

 vena cava. From the vena cava the blood pafTes into the 



anterior 



