PROFESSOR TURNER ON THE PLACENTATION OF THE SLOTHS. 75 
From the form of the uterus it was evident that only a single foetus was 
contained within the cavity, and that the head presented at the orificium uteri. 
I then made a mesial longitudinal incision through the posterior wall of the vagina 
and adjacent portion of the uterus, carefully dividing the several coats. In the 
part of the uterine cavity which was opened, a translucent envelope, the 
chorion, was exposed. The outline of the head of the foetus could now be dis- 
tinctly seen and felt. I then made an incision through the membranes, over 
the head of the foetus, with the view of extracting it, in order to pass a coloured 
injection into the foetal part of the placenta along the umbilical vessels. No 
fluid escaped when the membranes were divided. The foetus was now seen to 
be closely invested by a thin, semi-transparent membrane, which, as forming 
the immediate envelope of the embryo, I at first took to be the amnion. 
Further consideration, however, of its arrangement, which will afterwards be 
more fully described, satisfied me that it could not be that membrane, but a 
structure specially developed in connection with the foetus itself. 
A cut was now made into the umbilical cord, injecting pipes were intro- 
duced into the vein and into one of the arteries, and a prussian blue and gela- 
tine injection gently passed along these vessels into the placenta. When the 
coloured gelatine had solidified, the incision previously made into the uterine 
cavity was prolonged upwards to the fundus, so as to give a full view of the 
interior of the cavity. As is not unusual when an organ which possesses com- 
plex vascular arrangements is injected with two colours, I observed that both 
colours had run freely into some parts of the placenta, into others only a single 
colour,—sometimes the blue, at others the red had passed ; whilst a few limited 
areas had not received any injection at all. Opportunities were thus afforded 
of studying the vascularity of the placenta in every stage, from the perfectly 
injected to the uninjected state. 
The placenta was large in proportion to the size of the uterus, and took up 
about three-fourths of the entire surface of the chorion (fig. 3).* It corresponded 
to the fundus, and to the greater part of the anterior, posterior, and lateral sur- 
faces of the body of the uterus, reached to within two inches of the orificium 
uteri, and in its general form was dome-like, or bell-shaped. It concealed, 
therefore, the uterine orifices of the two Fallopian tubes. The posterior or non- 
placental part of the chorion which intervened between the lower edge of the 
placenta and the orificitum was translucent, and had slender ramifications of 
the umbilical vessels, which were filled with the blue injection, distributed in 
it, and forming networks with polygonal meshes, though in some localities the 
vessels were arranged in greatly elongated and compact networks. 
* To prevent any misunderstanding, I may state that in this and in my previous memoirs on the 
placenta, I use the term chorion, in the ordinary descriptive sense, to express the outer envelope of the 
fetus, without committing myself to any theory of the mode of production of this membrane. 
VOL exile PART I: U 
