PLACENTJi;. 



457 



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

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

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

 band, where the villi closely unite with the uterine pits 

 specially formed. 



4. Cotyledonary iilacmda (fig. 238). — This is characterised by 



'"'4% 



^ 



7 



.\ 



"^w* 





-ai 



Fig. 238. — Fcetus of Sheep. 



rfC'T 



AL, Allautoi?, seen beneath chorion ; Am, amnion ; P, P, placentas on chorion ; C, 

 umbilical cord ; al, al, extremities of allantoidean cornua. (Cliauveau.) 



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

 tlie cofi/i'-'duns, which fit into corresponding thick areas studded 

 wdth pits in the uterus. 



5. In the diffuse placenta (fig. 239) the allantois (a/) com- 

 pletely surrounds the embryo (F), and the whole chorion (Gh) 



