UTERUS. 



259 



ances consisting entirely of epithelium. Later they develop 

 numerous branches which go on dividing dichotomously. They 

 are made up of gelatinous tissue, which forms the axis, and a 

 layer of epithelium, which covers not only the villi, but also 

 the whole membrana chorii. In the larger stems of the villi 

 we find, instead of the gelatinous tissue, a fibrillar connective 

 tissue (Fig. 190). The epithelial coat is differentiated early 

 into two distinct layers (Fig. 191). The layer touching the 

 connective-tissue part consists of well-defined cells containing 



FIG. 191. 



Connective tissue^ 



Proliferation island 



Blood-vessel - 



Blood-vessel with 



cleated 

 blood cells 

 Ectoderm 

 of 



Proliferation island 

 t tangentially 



Transverse section of a human chorionic villas at the fifth mouth of pregnancy. X 300. 



clear protoplasm, and is known as the ectoderm layer of the 

 villus (Zellschicht of Langhans). The layer outside this con- 

 sists of cells which are not sharply marked off from one 

 another. It is made up of a continuous protoplasmic mass in 

 which there are numerous nuclei. We have here to do with a 

 syncytium, and we speak of this layer as the syncytium of the 

 chorionic villus. These two layers are separated fairly sharply 

 from one another, for the protoplasm of the syncytium has a 

 special affinity for acid dyes and stains more deeply, while the 

 nuclei are much smaller than in the ectoderm layer. 



Toward the middle of pregnancy (fifth month) the ectoderm 

 of the villi begins to degenerate, so that at the end of preg- 



