360 MINOT. [Vot. II. 
The diagram on Pl]. X XIX. will enable the reader to follow the 
ensuing descriptions. The general explanation of the diagram 
is given in the next section. 
The placenta is shaped somewhat like a mushroom: it has 
a very thick stalk, with a somewhat broader top. The top is 
bilobate, there being a deep fissure between the two lobes; this 
fissure persists at thirteen days (Fig. 8, 7) ; its fundus is the sub- 
placenta (Ercolani’s cotyledonary organ). The sides of the 
fissure are, of course, part of the surface of the placenta, mor- 
phologically speaking, and bear glands. The three zones of the 
placenta are well marked. In the outer zone the blood-vessels 
are very wide, with thickened degenerated epithelium ; the peri- 
vascular cells occupy the entire space between the vessels in all 
that part of the zone towards the muscularis and most of the 
space in the part towards the glands. Next to the sub-glandular 
zone, therefore, we see the vessels surrounded, each by its sep- 
arate thick perivascular coat, while the intervening tissue still 
consists of anastomosing cells, like those which in earlier stages 
occupied more of the space and which formed the only packing 
between the vessels at six days. The blood-vessels convert the 
layer, by their enlargement, into a spongy tissue, which has been 
described not only in the rabbit, but in other rodents; the ves- 
sels themselves have been generally described as glands, but 
the study of their development renders doubt as to their true 
character impossible. The vessels are partially empty in my 
preparations, but they contain very numerous leucocytes, nearly 
all of which have several nuclei apiece, which are conspicuous 
from their dark staining: there are a few red globules and here 
and there a little coagulum. As the corpuscles of the embryo 
are large nucleated bodies, there is no difficulty in distinguishing 
the foetal from the maternal blood, even in the upper part of 
the placenta, where the two circulations are juxtaposed. The 
middle or sub-glandular zone has undergone greater changes still. 
In it, as likewise in the glandular zone, the perivascular cells have 
almost entirely disappeared,! but they are, as it were, replaced 
1 This statement is perhaps not correct. There are certain spaces surrounded by 
epithelial or epithelioid cells to be seen in the upper part of the sub-glandular and in 
the lower part of the glandular zone; these spaces I have interpreted as parts of the 
glandular system, but they are perhaps maternal vessels with perivascular cells. The 
uncertainty as to their character could be probably removed by the examination of 
the ten days’ placenta, which presumably offers the intermediate stages. 
