FCETAL NUTRITION: THE PLACENTA 



501 



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

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

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

 fewer in number than over the serotina (Kastschenko 1 ). When the 

 blood-supply to the reflexa is reduced, the villi in relation to it 

 degenerate, and are compressed between the choriou and the apposed 

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

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

 of foetal villi between which maternal blood circulates. By the 



a, 



ca. sy, 



FIG. 155. Diagram of stage in the development of 'the human placenta. 

 (T. H. Bryce in (Juain's Anatomy, Longmans.) The "Haftzotten" are 

 attached to the surface of the decidua. The mesodermic processes are 

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

 lamella of syncytium. 



b., Attachment of a villus ; mes., mesoderm ; ves., vessels going to villi ; 

 sy., syncytium ; L.L, Langhans' layer ; a., cross-section of a villus ; 

 dec., decidua ; ca., maternal capillary. 



" Haftzotten " 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 foetal parts of the placenta. The most notable 

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

 mother-zone of the syncytium. Even the " Zellsiiulen " tend t<> 

 disappear from the tips of the villi, and their connective tissue 

 comes in contact with the decidua. Fibrinous changes are frequent 

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



1 Kastschenko, " Das menschliche Choriouepithel mid dessen Rolle bei der 

 Histogenese des Placenta," An-h. f. Aimt. ". I'liys., Anat. Abth., 1885. 



