Situation and Growth [Book IX* 



beautifully marked with the ramifications of blood- 

 vefiels. On the qucfide the blood -veffels can 

 fcarcely be obferved, as they are there very minute. 

 On the outfide of the placenta there is alfo an ap- 

 pearance like a divifion into lobes. The umbilical 

 cord is generally inferted, not into the middle, but to- 

 wards the edge of the placenta, which facilitates its 

 reparation after delivery. With the placenta, as has 

 been fuppofed, the arteries of the uterus have a com- 

 munication, by which, in the firft periods of geftation, 

 the foetus receives a ferous fluid, and in the later pe- 

 riods a large quantity of blood. 



It has alfo been taken for granted, that the arteries 

 of the umbilical cord communicate with the veins of 

 the uterus, and that thus a circulation of fluids is 

 maintained between the fcetus and the mother. Mr. 

 Hunter, however, after numerous experiments, has 

 adopted a different opinion. By a variety of trials by 

 injection he finds, that fluids thrown into the veflels 

 of the umbilical cord never get into thofe of the uterus ; 

 and on the contrary, thole thrown into the veliels of the 

 uterus find no admifiion into thofe of the umbilical cord ; 

 he therefore concludes, that the human placenta, as well 

 as that of quadrupeds, is a compofition of two parts inti- 

 mately blended, viz. an umbilical or infantile portion, 

 and an uterine portion. The former by maceration, is 

 found to confift of the ramifications of the veflels of the 

 umbilical cord, the other Mr. Hunter confidered as 

 an efflorefcence of the internal furface of the uterus, 

 which forms a membrane, fending numerous procefies 

 into the fubftance of the placenta ; this latter is the 

 membrana decidua, Mr. Hunter does not pretend to 

 fpecify the nature of the union between thefe two por- 

 tions of the placenta. 



Th* 



