506 VRO-GEN1TAL SYSTEM. 



late form, placed among a few connective fibres, and float in a 

 semi-fluid substance ; this is the magma reticulata of authors; 

 lastly, comes the anmion which forms the amnio tic pouch or 

 dive^ticulum, and contains the amniotic fluid (Fig. 143, 18). 

 The structure of the amniotic membrane recalls that of the 



Fig. 143. Envelope of the perfected ovum, placenta.* 



skin, with which it is continuous and whose origin it shares 

 (external fold of the blastoderm) ; in fact, it is composed of 

 an epithelial layer of pavement cells and a sort of dermis, 

 formed of cellular tissue, which contains some smooth muscu- 

 lar elements. 



Placenta, Nutrition of the Fcetus. The essential office of 

 the allantois consists in the formation, at the point where the 

 villi still exist and which also have an exaggerated develop- 

 ment (at the decidua serotina), the principal organ for the 

 nutrition of the fetus, viz., the placenta. In fact, at this 

 place the villi of chorion and allantois (chorio-allantoid villi) 

 are developed, spread out in every direction (placenta froii- 

 ) and ramify in the membrana serotina (Fig. 143, 22), 



* , Amniotic cavity (the body of the foetus is not represented; at 16 the 

 umbilical cord, cut at the point of attachment to the umbilicus at 17). o, lie- 

 mains of the umbilical vesicle. 18, Amnion. 19, The definite chorion. 20, Pla- 

 cental foetus. 21, Mucous layer, or uterine caduca. 22, Maternal placenta. 23, 

 Foetal caduca, or membrana reflexa. 24, Muscular tissue of the uterus. 



