36o 



Vetcrin a ry Obstetrics 



When the vascular laNer of the allantois develops, it grows out 

 and fuses with the amniotic chorion, which largel}- disappears 

 or becomes lost as a separate membrane, while the blood vessels 

 from the allantois grow out through it to constitute new tufts, 

 which soon attain an intimate relation with the blood vessels of 

 the uterus. 



AllaniOH- 

 Epi I helium 



Afembtaiia_ 

 Chorxt 



Cotyledon 



Gland 

 Duel 



Bloodvessels 



A 



■'H^ 



A- 





•vine ^ .-(r\ <^-5 r-N ^ - ' •_ 



Glands ^^ 





Afucosa 

 Uteri 



I 'teriiie 



Afuscular 



Ijiyer 



Bloodvessel 

 Fig. 78. Section through the chorion and uterine mucosa of the horse, at 

 9>^ months. Enlarged about .45-1. (Bonnet). 



The blood vessels of the fetus and tho.se of the mother do not 

 become continuous, but are constantly separated by three layers 

 of tissue, the endothelial layers of both the maternal and fetal 

 capillaries and an intervening layer of connective tissue. The 

 capillaries of the allantois become greatly branched and grow out 

 as villi which, sinking into the mucous membrane of the uterus, 

 come into immediate contact with corresponding capillary loops 

 from the uterine ves.sels and become closely adherent with each 

 other with extremely thin walls, through which there is a free 



