90 THE HUMAN DECIDUA. 



portion of the urachus between the bladder and the umbilicus remains 

 tubular, and in some instances it continues permanently in that condition, 

 so that urine can escape from the umbilicus.* 



Amnion. M. Serres f has again maintained that the amnion of the 

 human embryo, instead of being produced by a fold of the external layer of 

 the germinal membrane rising up and gradually enveloping the embryo, is 

 originally an independent vesicle outside the embryo, and that the latter 

 connects itself with it by dipping into, and eventually completely envelop- 

 ing itself with it. This view has been supported also by MM. Maignien 

 and Jacquart,J from the appearances presented by an early aborted embryo ; 

 but from Bischoff's account it would seem that both these observers as well 

 as M. Serres must, in the specimens examined by them, have overlooked 

 the true amnion, which from the early age of the embryos or from some 

 morbid change may have been obscured, and probably mistook for it either 

 the allantois or the umbilical vesicle. In his work on embryology, || 

 Bischoff states the various arguments in favour of the view that the 

 amnion of the human ovum observes the same mode of development as 

 obtains in other Mammifera. 



Chorion. Little requires to be said of the chorion of the human ovum. 

 It does not appear to present any essential difference from the chorion of 

 other Mammalia. Its formation around the ovum in rabbits and bitches has 

 been already described. In the former animals it is developed apparently 

 from the zona pellucida and the layer of albuminous matter by which the 

 zona is surrounded ; but in the bitch, in which no such albuminous deposit 

 occurs, it is developed (according to Bischoff) from the zona pellucida 

 alone. Bischoff believes that the human ovum, like that of the bitch, is 

 unprovided with an albuminous covering, and that the chorion in this case 

 also is formed directly from the zona pellucida ; but Mr. Wharton Jones is 

 inclined to doubt this statement. The villi of the chorion, as stated else- 

 where, are, at their first appearance, composed entirely of cells, and it is 

 not until the arrival of the allantois at the chorion, that vessels are 

 developed within them. 



Formation and structure of the decidua.. The subject of the formation 

 and structure of the membrana decidua, has within the last few years been 

 investigated anew by several physiologists, and the general tendency of 



* An account of the early development of the allantois of the human ovum is furnished 

 by M. Serres (An. des Sc. Nat. 1843 ; and Gazette Med. de Paris, 1843, p. 414), but it 

 contains nothing essentially new. Serres is of the same opinion with Langenbeck concern- 

 ing the close relation subsisting between the allantois and the corpora Wolffiana. For 

 Coste's view of the human allantois 3 vide Gaz. Med. 1843, p. 696 ; and for that of Velpeau 

 and others, see the account in the same journal of the discussion which ensued among the 

 members of the Academy of Sciences, after the reading of M. Serres's memoir. 



t Gazette Medicale, Juin, 1 843. 



J Gaz. Med. Novembre, 1843. Muller's Archiv. 1844, Jahresbericht, p. 144. 



|| Op. cit. p. 132 et seq. 



