No. 3.] UTERUS AND EMBRYO. 345 
lar decidua] cells, though the cells themselves scarcely differ 
yet from the ordinary connective tissue cells between the 
vessels. 
We find at this stage all the regions of the placental swell- 
ings, to be found in later stages, already definitely marked out. 
These regions are as follows :— 
1, PLACENTAL: subdivided into 
A, glandular zone. 
B, sub-glandular vascular zone with (a), sub-glandular 
zone with small vessels (4), outer zone with 
large vessels. 
2, PERI-PLACENTAL. 
3, OB-PLACENTAL. 
Each of these regions comprises two folds of the mucosa, 
viz.: the placental, the two folds next the mesentery ;! the perz- 
placental, the two lateral folds; and the 0b-placental region, the 
two folds opposite the mesentery. The three zones of the 
placental area persist and become much more marked in later 
stages, owing to the great divergence of the processes of his- 
tological differentiation in each zone. Of the two vascular 
zones, the szb-glandiular is characterized later by its very large 
multinucleate cells, while the outer zone is characterized by its 
crowded uninucleate decidual cells. All the regions and their 
subdivisions will be perhaps better understood by the descrip- 
tions and figures of the nine days’ uterus. (See below.) 
In my specimens, although the uterus seemed to be very well 
preserved, the blastodermic vesicles were completely shrivelled 
up; hence I could make no observations as to the relations of 
the embryo to the uterine wall. 
§ 3. Uterus of eight days and three hours. — It is un- 
necessary to describe the appearances at this age in detail, 
as they have been described already with admirable clearness 
and exactitude by Masquelin and Swaen, 114, 25-30. I have 
therefore only to confirm their account and refer to certain 
points on which my observations extend or differ from theirs ; 
it is also necessary to describe the extra-placental structures, 
which are left out of consideration by Masquelin and Swaen. 
1 Although this use of the term mesentery is etymologically indefensible, it seems 
permissible, and not likely to lead to misunderstanding any more than the etymologi- 
cally indefensible terms cell, endothelium, terminology, etc., etc. 
