82 



OBSTETRICAL PHYSIOLOGY. 



intestine, which proceeds very rapidly. It passes out where the ventral 

 laminae are still unclosed, in the region of the umbilicus, and reaches, 

 either mediately or immediately, the inner surface of the exochorion. 

 By the constriction of the umbilicus, it is separated into two portions 

 which communicate ; that within the body of the embryo is the saccu- 

 lated urinary bladder, with the uraclms or tube of communication. It 

 receives its vessels from the hypogastric artery ; these are spread out 

 as a vascular layer, especially upon that portion of its surface which 

 faces the exochorion. The vessels form a distinct layer — the endo- 

 cliorion. As a membrane it lines the inner face of the chorion, and is 

 reflected around the point of insertion of the umbilical cord, to be 

 spread over the outer face of the amnion ; in this way it transforms the 

 chorionic sac into a kind of serous cavity, in which the amniotic sac is 

 enclosed like a viscus. 



The inner, or amniotic layer, is so loosely united to the amnion, that 



Fig. 50. 



A, Foetus ; B, Cavity of the Amnion ; C, Cavity of the Allantois ; D, Um- 

 bilical Vesicle : 1, Chorion ; 2, Chorial Layer of the Allantois ; 3, Amniotic 

 Layer of the Allantois ; 4, Amnion ; 5, Urachus, the expansion of which 

 forms the Allantois ; 6, Pedicle of the Umbilical Vesicle. 



a slight dissection or inflation will readily detach it. When inflation 

 is practised, the separated membrane presents a wavy appearance, from 

 the presence of numerous cellular attachments it has with the amnion ; 

 as the inflation is forced these bands tear with a noise like the crackling 

 of parchment, and with care the whole of the portion, which is equal in 

 extent to the amnion, may be removed. The chorial allantois adheres 

 much more firmly, and in some parts it can scarcely be dissected away. 

 Inflation, however, demonstrates its existence and continuity with that 

 on the amnion ; for if, after opening the allantoid sac by cutting through 

 the chorion and the layer covering it, we introduce a tube between the 

 two membranes — which is easily done near a large vessel, a slight 

 inflation causes the air to penetrate between the allantois and chorion, 

 though only in the track of the vessels of a certain size, where the 

 adherence is slight ; a more powerful inflation will cause the air to 

 follow the smaller vascular ramifications, and render the membrane 

 still more apparent, but not at the points vrhere the vessels have almost 



