PLACENTA. 



433 



part only forming a discoidal patch ; but this grows out all 

 round, and invades the whole of the sub - zonal membrane 

 except at the poles. There is thus formed a broad placental 

 band, where the villi closely unite with the uterine pits 

 specially formed. 

 4. Cotyledonar II placenta (fig. 206). — This is characterised by 



y..^l 



Fig. 206.— F(Etu3 of Sheep. 

 AL Allantois, seen beneath chorion ; Am, amnion ; P, P placentse on chorion ; C, 

 umbiiical cord ; al, al, extremities of allantoidean cornua. (Chauveau.) 



the villi of the placenta being found in round scattered areas, 

 the cotyledons, which fit into corresponding thick areas studded 

 with pits in the uterus. 



5. In the diffuse placenta (fig. 207) the allantois (al) com- 

 pletely surrounds the embryo {F), and the whole chorion {Ch) 



2 B 



