FETAL MEMBRANES 347 



of the body cavity. The gut tract has the shape of a straight 

 tube occupying the long axis of the embryo and opening into 

 the umbilical vesicle. 



Fetal Membranes. 



Umbilical Vesicle. The umbilical vesicle represents that 

 part of the vitellus which has not been constricted off to 



FIGS. 102 AND 103. 



a, chorion with villi. The villi are shown to be best developed in the part of 

 the chorion to which the allantois is extending; this portion ultimately becomes 

 the placenta; b, space between the true and false amnion; c, amniotic cavity; 



d, situation of the intestine, showing its connection with the umbilical vesicle; 



e, umbilical vesicle; f, situation of heart and vessels; g, allantois. (Kirkes.) 



form the gut tract. (Figs. 101, 102, 103.) It furnishes 

 nutriment to the embryo for a short time and is then 

 largely cut off from the body. It gradually shrivels (Figs. 

 107, 108), and with that part of the duct external to the ab- 

 domen is cast off either before or at parturition. Vessels 

 develop in its walls and absorb the nourishment in it to be 

 conveyed to the embryo. But in the human being more sat- 

 isfactory arrangements for nutrition are soon made and its 

 function ceases. 

 Amnion. When the embryo has become depressed, as it 



