476 THE PHYSIOLOGY OF REPRODUCTION 



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 

 " Zellsaulen " tend to 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 



ca. sy. I). dec. ca. sy. 



FIG. 128. Diagram of stage in the development of the human placenta 

 (T. H. Bryce in Quairis 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. 



6., attachment of a villus ; mes., mesoderm ; ves. t vessels going to villi; 

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

 dec., decidua ; ca., maternal capillary. 



and in the mesoblast. The syncytium becomes very thin, and 

 occasionally tracts of it are stripped off. 



The decidua serotina, after reaching its full development 

 during the third month, is gradually thinned out. This may be 

 partly due to the stretching of the tissue by the increasing growth 

 of the uterine contents, but it would seem also to depend on 

 conditions of malnutrition caused by the blood-stasis (Bonnet), 

 and the choking of the lymphatics by the decidual development 

 (Webster). The resulting degeneration takes the form of a 



