588 
FORMATION AND USES OF 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 
o£ 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 oe 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 
hack to display its contents; d d , its lining membrane ; g , tufted surface of the 
chorion; g2, its internal aspect; h , h , amnion ; i , yolk-bag ; k, umbilical cord ; 
l, 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 
