580 PLACENTAL CONNECTION IN PERAMELES OBESULA. 
question as to the fate of the ectoderm may be left undecided for 
the present, especially since I have within the last few days 
received from Mr. A. G-. Hamilton a pregnant uterus of P. obesula 
containing an unattached blastodermic vesicle. The examination 
of this material will, I trust, throw light on the point in question, 
and also on certain other points in connection with the structure 
of the wall of the pregnant uterus. 
As a consequence of this union of foetal and maternal tissues 
the uterine wall exhibits certain structural modifications. The 
layer of columnar epithelium which forms the inner lining of the 
non-pregnant uterus can no longer be distinguished. It has 
degenerated apparently over the whole extent of the inner surface 
of the uterus. Also there are present a short distance below the 
surface of the mucosa, groups of large oval or rounded nuclei, 
which, in the region of the placental connection are larger and 
stain much deeper than in the remaining portions of the uterus. 
These groups of nuclei are probably derived by proliferation from 
the lining epithelium of the uterus. The uterine glands are large 
and well developed, their epithelial lining showing no signs of 
degeneration. 
The placenta is supplied with foetal blood by the allantoic 
vessels, which consist of a large vein, on either side of which is a 
small artery. These three vessels extend unbranched in the 
allantoic stalk. At its distal end the arteries branch out on the 
inner or coelomic surface of the vesicular portion of the allantois, 
while the allantoic vein is formed by the union of two main 
factors which accompany the main arterial vessels. The latter 
branch in a dichotomous manner on the inner surface of the 
allantois, each arterial branch being accompanied by a venous 
trunk as is characteristically found in the allantois. These vessels 
ramifying on the inner surface of the vesicular portion of the 
allantois can be traced round into the mesenchyme of the outer 
surface, and there they break up into capillaries. The capillaries 
become closely applied to the surface of the uterine mucosa and 
form with it a somewhat irregular interlocking system, since they 
dip down into the substance of the mucosa to form short villous 
