FGETAL NUTRITION : THE PLACENTA 



397 



The syneytivim is more pennaiient. 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 

 retlexa exists, the eaiiy 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 membi'ane 

 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 h&ve lost the 



b s I 



V 





i 







& 



/ 





Fig. 9R. — Part of an early human chorionic villus. (From Hofliauer's 

 Biolvgie der mgnschlicheii Plazentu, BraumuUer.) 



6, Biirstenbesatz with basal corpuscles ; s, syncytium ; /, Langhans' layei', 

 one cell dividing mitotically {I'). 



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

 man it is condensed superficially to form a layer which lieai's the 

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

 in fixed specimens, of a series of fine sfcri;e running perpendicularly 

 to the sui'face, and its structu.re and function have l)een much 

 discussed since it was first descrilied Ijy Minot.^ Some have denied 

 its existence during life, and asciilted it wholl)- to the methotl of 

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

 is when oljtained, the easier it is to demonstrate the stiiie by 

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

 Kastschenko looked on the striae as fine hairs which projected from 

 the surface of the cells, and Ijy tlieir vibrations ci'sated a stream in 

 the maternal blood of the intervillous spaces. In specimens stained 



' Minot, "Uterus and Embryo," Jour, of 3/orp/iol., vol. xi., 1889. 

 '^ Hofbauei', Bi'oiogie der men.vMiehen Plaienta^ Leipzig, 1905. 



