6O2 



PLACENTA 



dectduate, the villi of the placenta being so intimately con- 

 nected with the uterine mucous membrane that a part of the 

 latter comes away with it at birth in the decidua, or after- 

 birth, which is attached to the newly-born young by the 

 umbilical cord, consisting of the stalks of the allantois (a) 

 and flattened yolk-sac (ed) twisted together. The cord is 



FIG. 167. Diagrammatic longitudinal section of the foetus and embryonic mem- 

 branes of a rabbit. 



a. (on right) amnion ; a- (on left) stalk of allantois ; aL allantois with blood-vessels 

 c. embryo ; ds. cavity of the flattened yolk-sac (blastodermic vesicle) ; ed. endo 

 dermal layer of yolk-sac ; ed' . inner portion, and ed" . outer portion of endoderm 

 lining the compressed cavity of the yolk-sac ; fd. vascular layer of yolk-sac 

 //. placental villi ; r. space filled with fluid between the amnion, the allantois 

 and the yolk-sac ; sh. serous membrane ; st. margin of vascular area of yolk-sac 

 (From Balfour's Embryology, after Bischoff.) 



gnawed through by the parent rabbit, the blood-vessels being 

 compressed in the process ; and it soon shrivels up and comes 

 away at the navel or umbilicus, which represents the point 

 of connection between the foetus and the placenta. The. 

 intra-abdominal portion of the allantois is represented by a 

 cord or ligament, the urachus, which connects the navel with 



