154 APPENDAGES OF THE FCETUS. 



gous chorion; lastly, Needham, Diemerbroeck; Noorthwyck, with 

 Hoboken, Rouhault and Littre, have described it by the name of 

 chorion, while to the true chorion they give the name of allantois; 

 but these obscure descriptions were only fit to hinder the researches 

 of observers, and can in no respect be compared with that given of 

 it by W. Hunter. 



398. Formation. Impregnation determines in the uterus, a spe- 

 cific irritation, which is promptly followed by an exudation of co- 

 agulable matter, which concretes and soon transforms itself into a 

 kind of sac filled with a transparent and slightly rosy fluid. In 

 contact with the whole extent of the parietes of the uterine cavity, 

 this kind of bladder or membrane continues in some instances with- 

 in the origin of the Fallopian tubes, and always into the upper part 

 of the cervix, in the shape of soUd concrete cords; it never in a na- 

 tural state has any opening. 



399. The ovule, after having passed through the tube, necessarily 

 depresses the caducous membrane, so that it may glide on betwixt 

 it and the uterus, to the internal surface of which it at last attaches 

 itself; from this moment the pre-existing membrane is composed 

 of two portions: one, very large, lining the whole interior of the 

 womb, except the part which is in contact with the germ, bears the 

 name of uterine or external caduca; the other, very small, depressed 

 by the lower half of the fecundated vesicle, which it envelopes, con- 

 stitutes the reflected caduca, internal caduca or epichorion. The ex- 

 tent of the former augments in the same ratio with that of the 

 womb, and the aggrandisement of the latter necessarily follows the 

 growth of the germ. Therefore the cavity which separates them, 

 and which is nothing more than the altered cavity of the primitive 

 sac, is the greater, the nearer we are to the first periods of ges- 

 tation. 



400. The uterine caduca preserves a pretty considerable thick- 

 ness, especially in the vicinity of the placenta, until the close of 

 pregnancy; the epichorion, on the contrary, grows insensibly thin- 

 ner, so that at the period of labor it is sometimes of an extreme 

 tenuity. 



One, by sinking down into the other, at length comes to be in 

 contact with it, a little sooner or later, about the fourth month, 

 for example; after this, the two layers remain in a state of more or 

 less perfect contiguity until the expulsion of the after birth, with- 

 out however being even confounded together, notwithstanding the 

 assertions of Hunter and all others who have treated of this subject 

 since his day. It is evident, then, that this membrane is managed 



