FCETAL NUTRITION: THE PLACENTA 397 



The syncytium is more permanent. In the earliest human 

 ovum yet examined it already constitutes a considerable mass, and 

 a similar thickening over the whole or part of the circumference of 

 the blastocyst occurs early in all the Deciduata. Where a decidua 

 reflexa exists, the early proliferation appears to be related to the 

 excavation of the cavity in which the ovum lies. In discoid placentae 

 the mass is vacuolated, and maternal blood is contained in the lacunae. 

 In the later stages of pregnancy it forms an attenuated membrane 

 over the villi, and may wholly disappear at parts. The nuclei are 

 numerous, and most of the authorities agree on the absence of mitoses, 

 some holding that they divide directly, others that they have lost the 



I si I' 



FIG. 98. Part of an early human chorionic villus. (From Hofbauer's 

 Biologic der menschlicheii Plazenta, Braumiiller.) 



ft, Biirstenbesatz with basal corpuscles ; *, syncytium ; /, Langhans' layer, 

 one cell dividing mitotically (/'). 



power of division. The protoplasm has a foam-like structure, and in 

 man it is condensed superficially to form a layer which bears the 

 " Biirstenbesatz " or striated border (Fig. 98). This consists, as seen 

 in fixed specimens, of a series of fine stria? running perpendicularly 

 to the surface, and its structure and function have been much 

 discussed since it was first described by Minot. 1 Some have denied 

 its existence during life, and ascribed it wholly to the method of 

 preparation. But Hofbauer 2 has shown that the fresher a specimen 

 is when obtained, the easier it is to demonstrate the stria?, by 

 methods of staining, and, therefore, it is probably a vital structure. 

 Kastschenko looked on the striae as fine hairs which projected from 

 the surface of the cells, and by their vibrations created a stream in 

 the maternal blood of the intervillous spaces. In specimens stained 



1 Minot, "Uterus and Embryo," Jour, of Morphol., vol. xi., 1889. 



2 Hofbauer, Biologie der inenscMichen Plazenta, Leipzig, 1905. 



