1020 



EMBRYOLOGY. 



the allantoid surface assumes a sacculated or blistered appearance, due to the 

 numerous cellular bands that attach it to the amnion. These bands rupture 

 when iJie inflation is forced, and a noise is heard analogous to that produced by 

 the rumpling of parchment. With a little care, the whole of this portion of 

 the allantois — the extent of which equals that of the amnion — may be entirely 

 detached. 



" The degree of adhesion of the chorial allantois is more marked. Ordinary 

 dissection — which is easy along the first divisions of the cord — is much more 

 difficult towards the chorion, and soon becomes, if not impossible, at least very 

 arduous, if we desire to separate it. But here, again, inflation demonstrates the 

 existence of the membrane, and its continuity with the portion so easily dissected 

 from the amnion. If, after opening the allantoid sac by cutting through the 



Fig. 556. 



DIAGRAM OF THE DIFFERKNT HARTS OF THE FOSTAL HCRCE, TOWARDS THE MIDDLE OF GESTATIOK. 



P P, Placenta ; Ch Ch, chorion ; AT, external lamina of the allantois ; Al, internal lamina of 

 ditto ; o, urachus; e, cavity of the allantoid; A, amnion ; B, cavity of the amnion; Vo, remains 

 of the umbilical vesicle; V, vessels of the umbilical cord; F, foetus. 



chorion and the lamina lining it, a tube is introduced between the two membranes 

 — which is readily done near a large vessel — by a slight inflation the air enters 

 between the allantois and chorion, though it o'^ly follows the track of vessels of 

 a certain size, to the sides of which there is but little adherence. If the inflation 

 is pushed, the air — following the smallest vascular ramifications — renders the 

 membrane more apparent, though without detaching it from the points where 

 the vessels have almost become capillaries. 



" If, instead of injecting the air towards the ramifications, it is propelled in 

 the opposite direction, it will soon be perceived to extend towards the allantoid 

 portion of the umbilical cord, and insinuate itself between the amnion and the 

 allantois covering it — ^an evident proof of the continuity of the two layers which 



