THE MAMMALIA 305 



eventually disappears. Fig. 77 shows the final condition. 

 The allantoic villi have increased to an immense extent, and 

 their ramifications, covered by trophoblastic tissue, penetrate 



ms. m. 



Fig. 76 



Diagrammatic transverse section of a pregnant uterus, illustratirg an 

 enrly stage of placentation. all, allantois; atii, amnion; bv^ ulerine 

 blood-vessels; d cap, decidua capsulari.s ; em, embryo; lac^ lacuna; 

 l.tro, lateral or omphaloidean trophoblast ; /m^, secondary lumen of 

 uterus ; ins.m, mesometrium ; viu<:, muscular wall of uterus ; /V, pla- 

 centa; iro, trophoblastic tissue surrounding the allantoic villi; uazh, 

 stalk of the yolk-sac ; Ui, uterus ; ut.g; uterine glands ; yk, yolk-sac. 



the trager in all directions. Concurrently with the increase 

 of the allantoidean placenta, the maternal tissue above it 

 has disintegrated, and its place has been taken by tropho- 



II. U 



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