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 da3^s 

 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 characteristicall}^ 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 



