THE STRUCTURE OF THE HUMAN PLACENTA. G3 



longs to the decidua, and is continuous with tlie parietal division 

 through the medium of the cavities of the placental threads. 

 This portion of decidua has been named the central division of 

 the placental decidua, and the threads decidual bars. 



5. The function of the external cells of the placental villi is to 

 separate from the blood of the mother the matter destined for the 

 blood of the foetus. They are, therefore, secreting cells, and are 

 the remains of the secreting mucous membrane of the uterus. 



6. Immediately within the external cells of the placental villi 

 there is a membrane which I have named the internal membrane 

 of the villi. This membrane belongs to the system of the 

 foetus, and is the external or bounding membrane of the villi of 

 the chorion. 



7. Inclosed within the internal membrane of the placental villi 

 is a system of cells, which belong to the system of the foetus, and 

 are the cells of the villi of the chorion. These are the internal 

 cells of the placental villus. 



8. The function of the internal cells of the placental villi is to 

 absorb through the internal membrane the matter secreted by 

 the agency of the external cells of the villi. 



9. The external cells of the placental villi perform, during intra- 

 uterine existence, a function for which is substituted in extra- 

 uterine life the digestive action of the gastro-intestinal mucous 

 membrane. 



10. The internal cells of the placental villi perform during 

 mtra-uterine existence a function, for which is substituted in 

 extra-uterine life the action of the absorbing chyle cells of the in- 

 testinal villi. 



11. The placenta, therefore, not only performs, as has been 

 always admitted, the function of a lung, but also the function of 

 an intestinal tube. 



J. G. 



