DECIDUAL MEMBRANES 



379 



ized fibrin" which partially replaces it. In Fig. 380, cells of the deeper 

 layer of the chorionic epithelium may still be recognized, but these are 

 often lacking. 



Toward the uterine wall the placenta is formed by the decidua 

 basalis, which, like the decidua vera, includes a superficial compact layer 

 and a deeper cavernous layer. The compact layer, which is detached 

 with the placenta at birth, consists of connective tissue, blood vessels, 

 giant cells and decidual cells (Fig. 381). Some of the chorionic villi 



Amniotic epithelium. 

 Homogeneous layer. 



Leucocytes. <rj 



r 



Connective tissue of J| 

 the chorion. 



Chorionic'epithelium. 



Hyaline substance. * 



Syncytium 



Connective tissue 



Red corpuscles. 



^il- > " <s * >o **~>S 

 jQ&_ '" J-4/^ Chorionic villus. 



Blood vessels. 



FIG. 380. FROM A SECTION OF THE HUMAN PLACENTA AT TERM. X 200. 



have free endings toward this layer; others are extensively fused with 

 it, forming such masses as shown on the right of Fig. 381. 



The decidua basalis extends out among the villi in the form of septa, 

 which subdivide the mass of villi into lobes or cotyledons. (In the rumi- 

 nants, the cotyledons are widely separated by areas of smooth chorion, but 

 in man they are closely adjacent, with septa between them.) The septa 

 end before reaching the chorionic membrane, except at the placental 

 margin, where they form an enclosing wall. As the uterine arteries 

 approach the intervillous spaces of the chorion, they pursue a coiled course, 

 so that they may be cut several times in one section (Fig. 378) . They pass, 



