5S4 



PLACENTA 



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

 U7nbilical cord, consisting of the stalks of the allantois (a) 

 and flattened yolk-sac {ed, fd) twisted together. The cord 

 is 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 ntnbilicus, which repre- 



FiG. 156. — Diagrammatic longitudinal section of the fetus and embryonic mem- 

 branes of a rabbit, 

 (t. (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 ro"'. 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. m.argin of vascular area of yolk-sac. 

 (From Balfour, after BischofT.) 



sents the point of connection between the fo2tus and the 

 placenta. The intra-abdominal portion of the allantois is 

 represented by a cord or ligament, the urackus, which connects 

 the navel with the apex of the bladder, so that only a 

 small portion of the allantoic outgrowth, and not the whole 

 of it as in the frog, persists in the adult. 



