584 



PLACENTA 



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

 utiibilical 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 umbilicus, which repre- 



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

 branes of a rabbit. 

 u.. (on right) amnion ; a. (on left) stalk of allantois ; al, allantois with blood-vesselsL.; 

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

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

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

 pi. 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, after BischoflF.) 



sents 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 lirachus, 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 frpg, persists in the adult. 



