588 



FORMATION AND USES OP PLACENTA. 



the whole surface of the chorion, a number of little tufts shoot 

 out (fig. 325), which come into contact with the lining mem- 

 brane of the uterus ; and this is furnished with a multitude 

 of glandular follicles, which secrete a nutritious fluid that is 

 absorbed by the tufts of the chorion, and by them communi- 

 cated to the embryo. When the allantois is formed, it serves 

 to carry the blood-vessels of the embryo to the inner surface 

 of one part of the chorion ; and they shoot through this, so as 



Fig. 325. INTERIOR OF HUMAN UTERUS at the seventh week of Pregnancy : 

 b, outlet of the uterus, of which the walls c, c, c, c, laid open by incision, are turned 

 back to display its contents; d d, its lining membrane ; g, tufted surface of the 

 chorion ; g%, its internal aspect ; h, h, amnion ; i, yolk-bag ; k, umbilical cord ; 

 /, embryo. 



to dip-down, as it were, into large expanded vessels that extend 

 outwards from the walls of the uterus. In this manner is 

 formed, in all the higher Mammalia, the important organ 

 termed the Placenta; which essentially consists of the ramifi- 

 cations of the foetal blood-vessels contained in the Umbilical 

 Cord or " navel-string," ensheathed by prolongations of the 

 large vessels of the maternal uterus. In the Marsupials and 

 Monotremes (ZOOLOGY, 309 320), no placenta is ever 

 formed, the embryo coming into the world in a stage scarcely 

 more advanced than that represented in fig. 325. In either 

 case, the vessels of the embryo are enabled to absorb from 

 the blood contained in those of the parent, through the thin 



