TEE FOSTVS. 897 



or blistered appearance, due to the numerous cellular bands that attacb it to 

 the amnion. These bands rupture when the 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, whose extent 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 im- 

 possible, 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 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 only 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 directed 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 have been separated for the purpose of studying 

 them, but which are, in reality, onljr two portions of the same membrane 

 that forms a complete sac." ^ 



The cavity of this sac communicates with the bladder by means of the 

 urachus, a narrow canal contained in the amniotic portion of the umbilical 

 cord, and expanding towards the origin of the allantoid part (at d. Fig. 425), 

 where its walls are continuous, one part with the amniotic layer of the 

 membrane, the other with the chorial layer, after being prolonged as a 

 sheath around the cord (b). This arrangement shows the true character of 

 the allantoid cavity, whiish is evidently a kind of urinary reservoir, a 

 dependency of the bladder, whose fundus is prolonged to the umbilicus to 

 constitute the nrachus. The latter follows the umbilical vessels in the 

 amniotic portion of the cord, and soon expands in forming the allantoid 

 cavity. 



Steuctuee. — The allantois arises from the intestinal furrow, or otherwise 

 the included portion of the internal blastodermic lamina. It comprises a 

 slightly fibrous framework, and an epithelial layer. It carries the umbilical 

 vessels to its surface, from the umbilicus to the chorion. 



Allantoid Fluid. — This cavity contains a fluid, analogous to the liquor 

 amnii, and which has almost the same physical qualities. Analysis 

 demonstrates that, during the early months of foetal life, this fluid contains 

 a somewhat large proportion of sugar ; this gradually diminishes, and at last 

 disappears altogether. The fluid has been considered, towards the termina- 

 tion of gestation, as the urine of the foetus. 



HiPPOMANBS. — This name is given to small brown masses, more or less 

 numerous— though often there is only one — which float in_the_ allantoid fluid. 

 " These bodies, of the consistency of gluten, and elastic like it, are flattened, 

 thinner at the borders than towards the centre, oval or irregularly circular, 

 and about the diameter of a five-franc piece. It is difficult to explain the 

 1 F. Leeoq. ' Des Annexes du Fcetus.' 



