f^~ 



r 



'* '<m^ '^^ ''V* 



Fig. 538. — Diagrammatic Representation of Relationship of Ovum to Decidcja. 

 1, In latter half of first week; 2, a few days later; 3, a few months later, when placenta 

 is well defined (Webster) : a, Fetal mesoblast, showing indications of beginning extension 

 into trophoblast stalks in 1, actual extension in 2 and 3; h, tropho blast, being reduced in 

 3 and constituting here the layer of Langhans; c, trophoblast lacuna in 1, enlarged in 2 

 and 3 as an intervillous space; d, syncytium, seen in its earliest stage in 1; e, decidua; /, 

 maternal blood-sinus: g, endothelium lining maternal sinus; h, epiblastic covering of cord; 

 i, amniotic epiblast;y, umbilical vein; A", umbilical artery; Z, amniotic mesoblast; m, exten- 

 sion cf decidua on under surface of chorion at edge of placenta: n, large villus-stem. 



