AS\^ THP] FOETAL MEMBRANES. TX THE THTCK. ^Ql 



plained as iiioditicutions of this fm-iii. Thus, in Figs. 19, 20, and 21, 

 from an embryo of tlie eleventh day which correspond respectively to 

 Fiii's. 14, 15, and 1(5 of the ])recedini>' stage, the terminal portion of the 

 left allantoic arterv whicli runs alonu' the edofe AB in Fisf. 15 and 17, 

 runs along the axis on which the interallantoic septum is folded, and 

 consequently the septum formed by the left artery alone is very 

 small (ADK Fig. 21). Besides, in this example, the right allantoic 

 artery, running along the inner allantoic limb, is divided at the 

 point Z into two branches which, running along the free edges ZY 

 and ZX, emerge on the outer limb at the points Y and X respec- 

 ri\ely, and thus a somewhat complicated minor septum ZvSYXZ (see 

 also fig. 20 his.) is ]Droduced by that artery. 



By the eleventh or tAvelfth day the aJlantoic lobes come together 

 at the vegetable poJe of the egg. Consequently, the albumen-sac 

 or the ' .s'rtc placentoide ' of Duval is entirely cut off from the sur- 

 rounding space, as Duval says but contrary to Virchow's observation, 

 while its cavity is lined l)y an epil)lastic layer which has been con- 

 tinuous with that of the outer limb of the allantois. The leno^th of all 

 the allantoic septa is determined by the closure of the albumen sac, 

 Mud nil come together at that point where the allantoic lol^es finally 

 close. 



It is at this stage that the perforation of the plate-like connection, 

 before referred to, begins and it is a remarkable fact that for a few days 

 after, the amniotic fluid soon coagulates in alcohol or in Kleinenberg's 

 picro-sulphuric acid, just like the fluid in the albumen-sac. This 

 seems to be due to the presence of albumen which has found its way 

 through the perforations into the amniotic fluid. 



