VOL. XXII.J PHILOSOPHICAL TRANSACTIONS. 583 



and its relation to the other membranes, &c. after the parts were prepared and 

 dried, aaaa part of the chorion expanded ; bbb a line, expressing the edges 

 of the placenta ; ccc the amnios, which is united to d theallantois, at eee the 

 line of union ; f the cervix of the allantois ; g a hole at the fundus of the allan- 

 tois, whence the urine issued, and where the allantois was blown up ; h part 

 of that half of the allantois which lies under the line of union, and immediately 

 covered the foetuses, unless it be supposed that the amnios is continued under 

 the allantois ; ii two styles, or probes, thrust under the amnios ; they support 

 the allantois, and keep open the aperture **** of the amnios, whence the 

 twins come forth ; k part of the placenta, with some blood-vessels injected ; 

 LLLL the arteries of the navel-string filled with red wax ; mm the umbilical veins 

 filled with green wax ; n a communicant artery, by means of which all the 

 arteries of both navel-strings were filled at once, and the veins were filled by 

 one injection in like manner ; o a pin that keeps out the amnios, where from 

 the edge of the placenta it runs partly to the line of union, or adhesion, and 

 partly over the placenta ; p part of the chorion at the edge of the placenta, 

 where it runs under the amnios on the placenta ; q a pin, that by a thread helps 

 to pull open the aperture of the amnios; rkr the urachus, lying between the 

 arteries ; aaaa fibres, or vessels, which fasten the allantois to the chorion. 



Fig. 3 exhibits a side-view of the same preparation, that the insertion of the 

 urachus, &c. may be better seen. Note that a and all the same letters in these 

 three figures denote the same parts in every one. s shews the course of the 

 urachus r at f in pricked lines ; t part of the amnios raised from the edge of 

 the placenta, to discover the placenta k and v ; v that part of the allantois 

 which is below the line of union, near its neck f. 



Fig. 1 shews an entire allantois of a very small abortion. Note, this allan- 

 tois was easily separated from the other membranes between which it lay ; and 

 the amnios remained an entire bladder or membrane under the allantois. 



It is objected by some that what is called the line of union can be no real 

 thing. As to this I do not know whether the allantois of twins may not require 

 such a conjunction to sustain, and keep steady a greater quantity of urine : nor 

 can I resolve whether the allantois of twins (like that of a single foetus in fig. 1) 

 may not be distinct and separable from the amnios, but which I could not dis- 

 cover. However, the reasons why such a line was figured, are these: 1. 

 Although I used more force, with equal care, to separate the allantois from 

 the amnios, in this place, than in any other, (where nevertheless the separa- 

 tion was very easy,) yet I could not divide these membranes further than that line. 

 2. This line seeming so regular as to divide the allantois into two equal parts, 

 I could not take it to be the effect of chance, or my separation. 3. The part 



