CH. vi PREGNANCY PAKTUEITION PUEEPEKIUM 223 



works on placentation. Sfameni* disagrees with Ercolani on one 

 point only, the origin of the decidua, which he derives from the 

 proliferation of the epithelium, whereas Ercolani derives it from 

 the connective tissue of the uterine mucosa. The layer of 

 tissue which immediately surrounds the ovum settled in the 

 mucosa of the uterus has received from modern writers the name 

 trophoUast, and from it the syncytium and Langhans's stratum of 



the chorionic villi are rightly 

 considered to arise. This layer 

 is, according to Sfameni, merely 

 decidua, which, owing to the fact 

 that it is in immediate contact 

 with- the ovum, shows greater 



FIG. 86. Ovum of about four weeks. 



Fio. 87. Ovum at the end of two months . 



FIG. 88. Ovum in the course! of the third month. 



activity in proliferation, because to it is assigned the task of 

 enveloping the ovum. 



The blood-vessels in the region of the chorion laeve become 

 obliterated; in the region of the chorion frondosum, on the 

 contrary, they develop at the same rate as the proliferations of the 

 villi, and extend to the smallest offshoots thereof in the form of 

 an arterial capillary, coil-like network which gives rise to a small 

 vein (Fig. 89). The villi of the chorion frondosum, which are rich 

 in vessels, may be compared from the physiological point of view 



