ON THE REPRODUCTIVE SYSTEM IN ANIMALS. 
523 
conception, the impregnated uterus throws out a coating of effused 
lymph; this coating wholly covers the internal surface, shutting 
the os uteri, and forming the whole into one closed cavity. In 
this peculiar condition the uterine mucous membrane is termed the 
' decidua.’ At a later period, the decidua consists of two distinct 
layers; the one lining the uterus is termed "tunica decidua uteri;’ 
and the one immediately enveloping the ovum, ‘ tunica decidua 
reflexa.’ I ought to have mentioned that, during the passage of 
the ovum through the Fallopian tube, it receives an additional layer 
of albuminous matter, secreted from the walls of the tube; this 
becomes surrounded by a fibrous membrane. This special en¬ 
velope, termed the * chorion,’ is of very great importance, being the 
medium of nutrition to the embryo in its early stages. From the 
entire surface of the chorion villous processes project. These pro¬ 
cesses serve the purpose of absorbent radicles, drawing in the fluid 
afforded by the parent, and the contained embryo appropriates 
the fluids thus imbibed for its own nourishment. The first organ 
of the foetus that is formed is the heart, which very soon presents 
a pulsating point; next, the brain and liver are formed ; the foetus 
then sends forth vessels to the uterus, and by those vessels an 
immediate connexion is formed between the foetus and mother. 
As the term of pregnancy advances, the membranes already re¬ 
ferred to become altered in character; they are the medium of 
communication between the mother and foetus, and, constituting 
this connexion, they are termed the placenta. The manner in 
which the placenta and uterus are connected is very different in 
the several species of animals. In the mare, the placenta is 
attached to the whole internal surface of the uterus; in the cow, 
the internal surface of the uterus presents a great many prominent 
points or eminences: corresponding projections appear on the foetal 
portion of the placenta, each of which is furnished with a papillous 
surface, the projecting part of the one being inserted into corre¬ 
sponding depressions in the other. The connecting parts, as above 
described, are the true placenta, and are termed f cotyledons.’ 
They are very numerous—above fifty in common; they vary in 
size from one to four inches in diameter, and are intimately con¬ 
nected with the foetus by their respective vessels. 
It has thus been shewn that the placenta owns a maternal and 
a foetal portion. In the maternal portion the arteries are furnished 
by the uterus;—they divide into numerous ramifications—anas¬ 
tomose freely with each other—and pass into the placenta in a 
screw-like form; hence physiologists of the present day name them 
* curling arteries.’ The blood is returned to the uterus from the 
placenta by short straight trunks; they pass obliquely from the 
placenta, something analogous to the manner in which the ureters 
