360 



J^ctei'inarv Obsfctrifs 



W^hen tlie vascular la> er of the allantois develops, it grows out 

 and fuses \'\ith the amniotic chorion, which largeh' 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. 



Allaiiloic 



C/ioru' 



CotvUdon 





Bloodvessels 



f1 





^Allantoic 

 Chart on 



VIn tne ^_ 

 Glands X, 



6 



'^ Mucosci 

 VUti 



IHetine 



~^' Muscular 



Laycr 



Mnudvei--el 

 Fic. 7,S. Section through tlie chorion and uterine mucosa of tlie horse, at 

 9^2 months. Enlarged about .45-1. (Bonnet). 



The blood vessels of the fetus and those 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 ti,ssue. 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 vessels and become closely adherent with each 

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



