FGETAL NUTRITION: THE PLACENTA 501 



becomes l)ranclie(l like a tree (Fig. 154). At first they are equally 

 distributed over the chorion, Init the villi in relation to the reflexa do 

 not branch so much, and even at the end of the first nicjnth they are 

 fewer in numlier than over the serotina (Kastschenkoi). When the 

 lilood-supply to the I'eflexa is reduced, the villi hi relation to it 

 degenerate, and are compressed l)etween the chorion and the apposed 

 decidua reflexa and vera. Over the serotina they continue to branch 

 and form the fretal part of the placenta, which is essentially a mass 

 of fcetal villi Ijetween wliich maternal l;)lo(xl circulates. By the 



Fig. 15.'). — Diagram of stage in the development of the human placenta. 

 (T. H. Bryce in (ifuain's Ajiatujiii/, Longmans.) The " Haf tzotten " are 

 attached to the surface of the decidua. The mesodeiinic processes ai'e 

 everywhere covered by a single layer of cells (Langhans' layer) and a 

 lamella of syncytium. 



h., Attachment of a villus ; rues., mesoderm ; ves., vessels going to villi ; 

 SI/., syncytium ; L.I., Langhans' layei- ; c, cross-section of a villus ; 

 der., decidua ; i:a., maternal capillaiy. 



" Haftzotteii " the spongy mass is attached to the decidual surface. 

 The attached ends may excavate the decidua to some extent, but 

 there is no great degree of penetration (Fig. 155). 



As pregnancy advances, marked degenerative changes occur in 

 the maternal and fVetal parts of the placenta. The most notable 

 change in the villi is the gradual disappearance of the cytolilast, the 

 mother-zone of the syncytium. Even the " Zellsiiulen " tend to 

 disappear from the tips of tlie \\\\\, and their connective tissue 

 comes in contact with the decidua. Fibrinous changes aie frequent 

 in the remnants of the cytoblast and in the mesoblast. The 



' Kastschenko, " Das menschliche Choriouepithel und de.ssen Rolle bei der 

 Histogenese des Placenta," Aixh. f. Anat. -i. Phij.^., Anat. Abth., 1885. 



