260 MICROSCOPIC .I.V.I TOMY OF Till: < 



nancy it is almost entirely wanting and the villi are covered 

 only bv the syncytium. In certain places there are thickenings 

 formed in the membrana chorii as well as in the villi. In the 

 apices of the latter they are called cell nodes. Local thicken- 

 ings in the syncytium are called proliferation islands 

 (Fig. 191). Toward the end of pregnancy the syncytium 

 also vanishes, and in its place there is a homogeneous, refrac- 

 tive, faintly staining substance containing numerous empty 

 spaces, and known as canalized fibrin or hyaline (Fig. 192). 



FIG. 192. 



' Oblique section 

 - --iif xuncytium 



A \ - .>:-: / ''"- 



Fibri 



-J 



From a section through a human placenta at the fifth month of pregnancy. X 80. 



This substance increases with the age of the placenta, but its 

 origin and significance are by no means clear. Although there 

 is no doubt that the villus ectoderm is of embryonic origin, 

 there is still some question as to the derivation of the syn- 

 cytium. 



Between the villi we find so-called intervillous spaces which 

 contain blood. The villi are thus surrounded by blood on all 

 sides. The views held as to the origin and significance of these 

 intervillous spaces are still much at variance. This problem is 



