19G GENERATION 



proportion) passing through the liver of a foetus than through that of 

 the adult : this is also similar to the Amphibia. 



Modes of Maternal and Foetal Communication. 



It would seem that the communication between the mother and the 

 fetus is carried on in two ways, and in the two combined. In the 

 human subject it is entirely by extravasation 1 ; in the mare and sow by 

 apposition of vessels ; and in the bitch and cat by both ways combined. 



When a calf is about half the size of a mouse, the membrane [chorion] 

 on which the cotyledons are placed, passes through the whole horn of 

 the uterus, or lines the whole. Where the embryo is situated the coty- 

 ledons are pretty well formed or risen, and as the membrane recedes 

 from this they are fainter and fainter ; and towards the two ends they 

 are not observable. The external membrane on which the cotyledons 

 are formed is spongy, and would appear to act like a cotyledon. This 

 [membrane] is lined everywhere by a thin membrane [allantois], which 

 is slightly attached to it : this [allantoic] bag is above half-full of water 

 [serum]. The foetus lies in a circumscribed bag [amnios] about four 

 times its own size, filled with water, and slightly adhering externally 

 to the inside of the former. The chord goes out and appears to per- 

 forate the proper bag [amnios], as also the lining [allantois], and 

 divides into two portions ; one runs along the spongy chorion towards 

 one end, the other towards the other end 2 . 



Of the Situation of the Foetus and Membranes when there is but one 

 in the two-horned Uterus. 



In a sheep that had one lamb in the uterus, it was in one of the 

 horns. I observed two spongy parts in the ovarium of that side, and 

 that the membranes passed into the other horn, and were there attached 

 to the cotyledons as in the same side where the fetus was 3 . 



Experiments on Soivs. 



December 24th, 1781. — In a sow which took the boar on Tuesday 

 and was killed the Thursday sennight following, in the morning, which 



1 [By the maternal blood passing into cavities which have lost the form of vessels, 

 and form the ' sinuses' mentioned at p, 192. See Animal Economy, pp. 60-70.] 



" [Hunt. Preps. Nos. 3499, 3500, 3501.] 



3 [The experiments on ewes to determine the effects of impregnation on the ovaria, 

 are printed in the Physiological Catalogue, vol. v. p. 120, from a copy of the MS. 

 supplied to me by Mr. Clift, whilst I was engaged in describing the Hunterian pre- 

 parations, Nos. 3481-3495. The ovarian ovum, of which Hunter appears to have 

 been in quest, being pellucid, colourless, and much more minute than he anticipated, 

 escaped lus observation.] 



