72 



OBSTE TRIG A L PH YSIOL OG Y. 



found. The inner face is 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 chorion may be divided into two laminae, the outer of 

 which has been called the exochorioii^ and the inner the endochorion. 

 From the endochorion are derived the vessels which pass to the villi, the 

 chorion itself being destitute of vessels until the allantois is developed. 



FiZ- 37- 



IcETAL Membranes of the Goat at Full Time: Twins. 



A, Cervix of the Uterus ; B, Left Cortiu ; C, Right Cornu ; D, Allantois of one of the 

 Foetuses ; E, Amnion of ditto ; F, Portion of the Uterine Wall left at the middle of its 

 Body, where the Foetuses come in contact ; G, Union of the Two Chorions at the 

 Cervix Uteri. 



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 arrangement closely resembles that of vegetables, each cell 

 containing a distinct nucleus ; the villi have the same texture, but their 

 cells are filled with a granular matter. The strength of the membrane 

 is greatest in the early ovum ; it is formed by the zona pellucida^ which is 



