370 MINOT. [Vou. II. 
deep; it is completely filled with the ingrowth of mesoderm and 
its accompanying large vessels. At the bottom of the fissure 
next the outer placental zone, 0.2, is situated the sub-placenta, 
sb.~l. The section drawn in Fig. 9 does not show the connec- 
tion between the fissure and sub-placenta, which appears in sec- 
tions 208-214 of the same series. The thickness of the meso- 
dermic covering of the placenta has increased very considerably, 
and the larger vessels are now provided with well-marked mus- 
cular as well as endothelial walls. Many of the foetal vessels 
run in spaces which stretch down nearly vertically from the 
placental surface; in some cases the vascular columns can be 
followed until they enter a cap of epithelium which forms a sort 
of U. These relations suggest the presence of a series of foetal 
villi covered in part by a very thin epithelium, and covered at 
their tips by a relatively thick epithelium. This interpretation 
has been discussed in the previous section. Beside the normal- 
looking epithelium, we find the degenerated glands not much 
changed from eleven days. The sub-glandular zone, sgZz, 
shows further enlargement of the blood-vessels, so that they are 
now larger than those of the outer zone, 0.2, thus reversing the 
earlier relative proportions; the multinucleate cells have in- 
creased in number and size, and contain more nuclei than at 
eleven days; they occupy all, or nearly all, the room between the 
vessels. Towards the outer zone the vessels are surrounded by 
the uninucleate perivascular cells, but the intervening tissue 
consists of multinucleate cells, so that there is a boundary re- 
gion which cannot be assigned strictly either to the subglandu- 
lar or to the outer zone. The outer zone, 0.2, is solidly packed 
with perivascular cells. 
The sub-placenta, s0.p/, lies still deeper than before, being 
now close to the outer zone. Its epithelium is undergoing 
hyaline degeneration, and accordingly is irregularly thickened, 
and its nuclei are multiplied: the substance of the layer stains 
deeply with eosine. 
The peri-placenta, P, differs from that at eleven days, princi- 
pally in having the perivascular cells as a solid packing through- 
out the whole of its extent, except just where it adjoins the 
glandular layer of the placenta. As at eleven days, its covering 
epithelium is reconstituted on the part towards the sub-placenta, 
and is in the phase of degeneration towards the placenta. 
