THE PLACENTA 



429 



Canalized fibrin consists of a granular eosinophilic mass which is 

 pierced by many narrow clefts, hence the name. 



The Chorionic Villi. These innumerable processes form the 

 greater portion of the placental tissues. They vary in size from 

 the broad main stems to the very slender terminal branches of the 

 floating villi. In the early condition of the placenta (fourth or 

 fifth month of pregnancy) the villi are clothed with a double epi- 

 thelial layer, of which the superficial takes the form of a syn- 



?:'*" : --.v': 



1TIES 



FIG. 346. THE CHORION OF THE HUMAN PLACENTA AT THE SEVENTH MONTH. 



4 cellular layer ; ep, remnants of the epithelial layer ; /ft, canalized fibrin ; mes, meso- 



dermal stroma. x 445. (After Minot) 



cytium, derived, according to Keibel,* from the endothelium of the 

 maternal blood vessels ; the deeper consists of a cellular layer, the 

 cells of Langerhans. At later periods (seventh month to full 



* Anat. Anz., 1889. 



