'II IK REPRODUCTIVE SYSTEM 



379 



tissue covered by a layer of epithelium. The connective tissue is of 

 the mucous type and serves for the transmission of numerous blood- 

 vessels. In the villi of early pregnancy the epithelium consists of an 

 inner layer of distinctly outlined cells and an outer layer of fused cell 

 bodies — a syncytium (Fig. 270, A, a) — containing small scattered 

 nuclei. The villi of the later months of pregnancy have no definite 

 epithelial covering, but are surrounded by a delicate homogeneous 

 membrane, probably the remains of the syncytium. At various 

 points on the surface of the villus are groups of nuclei. These stain 



"Giant" 



cell 



.^.r. 





^'v.'."*^:; •.-. :■ 



f 



•;:;:^F>'''-«^ 



-> 



A' 



Syncytium 



3^ ''iit-V-.. Ikt^J 



Trophoder:;! 

 mass 



Stroma of 

 villus 



Fig. 269. — Section of Chorion of Human Embryo of one month (9 mm.). (Grosser.) 



intensely, are surrounded by a homogeneous protoplasm, and form 

 knob-like projections above the general surface of the villus. They 

 are known as cell patches, or more properly as nuclear groups (Fig. 

 270, c), and represent remains of the nuclei of the epithelium of the 

 younger villus. Between the nuclear groups the villus is covered 

 only by a thin homogeneous membrane. Small villi usually resemble 

 more closely in structure the younger villus, being frequently covered 

 by a nucleated syncytium. Portions of the syncytium, especially 

 of older villi, sometimes become changed into a peculiar hyaline sub- 

 stance containing numerous channels. This is known as canalized 



