THE PLAOENTATION OF PERAMELES. 387 



GENERAL SUMMARY OF RESULTS. 



Before entering upon the detailed description of the various 

 stages, it may conduce to clearness if a brief resume of the main 

 facts of placental development be here presented. 



I. Changes in the Uterine Wall. 



The mucosa undergoes marked hypertrophy over its whole 

 extent ; the uterine glands increase both in transverse diameter 

 and in length ; the interglandular connective tissue forms a 

 loose open network of anastomosing cells^ and becomes per- 

 meated by abundant lymph ; the vessels of the mucosa in- 

 crease greatly in size and in number. These changes in the 

 coriura are accompanied by the transformation of the whole 

 of the uterine epithelium into a vascular syncytium. This is 

 ushered in by the disappearance of the cell outlines between 

 the cells and the active proliferation of the nuclei. The 

 uniform nucleated syncytial layer thus produced increases in 

 thickness by the growth of the protoplasm ; the nuclei also 

 increase in number, and eventually become, in greater part, 

 grouped together in nests, situated in lobular projections of 

 the deeper surface of the syncytium. At the same time 

 maternal capillaries pass up between the syncytial lobules, 

 penetrate the syncytial protoplasm, and form a network on 

 and just beneath its surface. 



The uterine wall is now prepared for the attachment of the 

 embryo. 



II. Embryonic Changes. 



(a) Fixation of the Embryo. — (1) The embryo becomes 

 attached to the maternal syncytium by means of the enlarged 

 ectoderm cells over the discoidal area of true chorion with 

 which the allantois fuses. The ectoderm, when the attach- 

 ment is complete, consists of a single layer of greatly enlarged 

 cells, roughly cubical or columnar in shape. Their irregular 

 outer ends accurately fit into the irregularities of the surface 



