VOL. XXII.] PHILOSOPHICAL TRANSACTIONS. 579 



as in De Graaf's cut, and its insertion appear plain on the placenta, which 

 yet cannot be discovered in his figure, which is quite irregular, and I take it to 

 be fictitious. As for the urinary membrane g, in his figure, it seems to be the 

 allantois of a colt (where Needham says, the umbilical cord runs through the 

 urinary membrane) not less absurdly added to the secundines of a human foetus, 

 than the secundines of a whelp are to a like foetus by Vesalius. 



Lastly, it is evident that De Graaf knew nothing of the true shape of this 

 membrane, and that he had never seen one entire, because he assents to Need- 

 ham's description of it as true ; which yet is false in several particulars. For 

 1st, the urinary membrane does not cover the whole foetus, as he affirms, but 

 only that part of it which respects the chorion, and does not lie on the placenta ; 

 for the allantois can be extended at farthest only to the edges of the placenta, 

 where the amnios and chorion are so closely joined by fibres, that no membrane 

 can come between them. Wherefore, 2dly, the allantois is not every where 

 fastened to the chorion. And consequently, 3dly, the allantois cannot be of 

 the same shape that the other membranes are of, nor be like the allantois of a 

 colt, which contains the foetus in the amnios ; all which Needham asserts. In 

 short Dr. Needham had seen only pieces of the urinary membrane, but never 

 an entire one, and so could only guess at its shape, &c. from what he had ob- 

 served in mares and gland uliferous animals. He might have made a better guess 

 at the figure, site, &c. of a human allantois, from that of a whelp, which does 

 not every where encompass the foetus as he observes. 



Bidloo, in most of his figures of the secundines, marks some vestiges of the 

 urinary membrane ; but in any of these figures are only to be seen broken pieces 

 of one placed so confusedly, that no idea of its size, shape, or situation can be 

 formed from them. I must own that the membranes of the secundines are often 

 so torn, that no art can exhibit an entire allantois. However, among the many 

 secundines that have come under the hands of anatomists, several no doubt must 

 have been entire enough for a fuller discovery than they have made, had it not 

 been by their ways of proceeding, viz. by knife, fingers, or blowing under the 

 chorion, impossible to discover any thing plain or satisfactory, even in the 

 fairest subjects. 



I come now to answer the objections of those who still deny a urinary mem- 

 brane to a human foetus. The difficulty of finding this membrane, is by no 

 means an argument against its existence ; but a woman that dies big with child, 

 is so fair a subject for the discovery of three membranes, that I wonder Parey, 

 having such an opportunity, could find only two. Dr. Tyson observed three 

 membranes in a like subject ; and after the chorion was divided and laid aside, 

 he saw two bladders, containing liquors of different colours ; which on pressing 



4 £ 2 



