THE ANNEXES OP THE F(ETUS 21 



The function of the liquor amnii is to protect the foetus 

 against external injuries ; abnormal movements and mechanical 

 influences are modified by it to such an extent as to protect 

 the foetus against violence. During parturition, on rupture of 

 the foetal membrane, it lubricates the vagina and expedites the 

 passage of the foetus. 



ALLANTOIS. 



Between the chorion and amnion, as eontimiation of the 

 urachus, lies a sac, which, on account of its sausage shape, is 

 termed aUantois {aXXdZ, sausage). The urachus forms the 

 tube of communication between the aUantois and the urinary- 

 bladder. The external face of the aUantois rests against the 

 internal face of the chorion. When the isolated and emptied 

 sac of the aUantois is inflated, a bicornual, irregularly cylin- 

 drical sac is formed. The head of the foetus lies in the 

 shortest but larger cornu ; the longer cornu of less diameter 

 forms that portion of the aUantois where the posterior ex- 

 tremities are. (Lecoq.) 



The allantoid sac contains : The allantoid liquid, the 

 foetal urine, which increases toward the end of gestation. 

 It is a whitish, foamy, thin liquid of neutral reaction. In the 

 beginning of gestation it is colorless ; later, yellow or brownish. 

 Its quantity near pregnancy amounts to 8 to 15j 1. 



Eobin proved the absence of grape-sugar, oxalates, albu- 

 min, mucus and allantoidin in the allantoic liquid. 



UMBILICAL VESICLE {vesicula umbilicalis). 



The umbilical vessel is a provisory organ arising from the 

 embryonic gut. It develops rapidly in the first days following 

 conception in all mammalia, soon ceases to grow, and finally 

 atrophies. 



As soon as the aUantois shows itself, it loses its import- 

 ance as a nutritive organ of the foetus, since the aUantois 

 carries the foetal vessels to the chorion, and now, by the 

 formation of the placentae, the foetus is nourished from the: 

 mother. 



