312 A. A. W. HUBRECHT. 
region, thicker opposite, and thickest at the sides. The dark 
tint of shading of the uterine tissue in fig. 1, immediately 
adjoining the lumen, is intended to indicate that in this region 
the interglandular connective tissue is much more compact 
than further outwards, where the cells have a more paren- 
chymatous aspect, and where the capillaries and small blood- 
vessels can on account of this be more easily traced than in 
the more compact inner portion. A true submucosa can 
hardly be said to be present. On the deepest regions, to 
which the glands descend, the muscular layers (inner circular, 
and outer longitudinal, with outermost thin sheath, in which 
fibres run at right angles with each other, and at angles of 
45° with those of the foregoing) immediately follow. The 
larger blood-vessels are seen to take their course in these 
muscular layers, and after parturition the uterus, even when 
it has shrunk to comparatively small dimensions, may easily 
be recognised from one in which parturition has not yet taken 
place by the considerable distension of which these vessels 
then show most evident traces. 
If we now compare a section through the region of the 
uterus where the blastocyst is found, with the foregoing, the 
most obvious difference is the change in the shape of the 
lumen, which is considerably reduced and modified through a 
process of very copious cell-proliferation that has taken place 
in the interglandular cellular stroma of the region diametri- 
cally opposite the mesometrium. The lumen in transverse 
section has exchanged its ; shape for a T shape. The pro- 
liferation here mentioned may be indicated as decidual neo- 
formation. It is not a process of perivascular proliferation, 
but of active increase of the subepithelial connective tissue, 
forming that part of the stroma of the mucosa which is indi- 
cated by a darker tint in fig. 1. This decidual metamorphosis 
is not restricted to the point opposite the mesometrium, but it 
also affects the interglandular tissue of the adjoining lateral 
uterine walls. The consequence of this active process is the 
change of shape of the lumen which was already mentioned, 
and is represented in fig. 2. At the same time more important 
