76 



OBSTETRICAL PHYSIOLOGY. 



lined by the external layer of the allantois, to which it is closely 

 adherent except at the insertion of the vascular cord, where there exists 

 a kind of conical infundibulum occupied by the umbilical vesicle. On 

 this surface the umbilical arteries and veins ramify, their minute 

 divisions traversing the membrane to form the placental villosities. The 



Fig. 46. 



FcETAL Membranes of the Cow at Mid-term. 



A, Uterus opened on its left side ; B, B, Cotyledons of the Uterus ; C, C, Placen- 

 tulse ; D, D, Allantois ; E, Vesicle of the Urachus ; 7, Amnion ; G, Um- 

 bilical Cord. 



chorion may be divided into two laminae, the outer of which has been 

 called the cxochorion, and the inner the endochorion. From the endo- 

 chorion are derived the vessels which pass to the villi, the chorion itself 

 being destitute of vessels until the allantois is developed. The structure 

 of this envelope is that of a delicate cellular membrane, traversed by 

 the vascular ramifications of the placenta. In many places its cellular 



