160 APPENDAGES OF THE FCETUS. 



be exactly the same throughout: so that the thesis of Phil. Beclard, 

 and M. Meckel's Manual of anatomy contain several manifest errors 

 on this subject. 



Hewson, and many who preceded him, have asserted that the 

 chorion is formed of several coats, which, being early applied to 

 each other, come at last to constitute only a single one; that the 

 placenta results from the unfolding and thickening of these laminae, 

 from which each of the umbilical vessels receives a sheath, &.c. 

 But I have already shown, in 1824, that the reason of this 

 supposition probably depends upon the presence of a concrete 

 lamellar layer, which indeed does invest the vascular roots of the 

 placenta, and separates it from the external surface of the chorion. 

 At present I may add, that if Ruysch, Haller, and so many others, 

 supposed the chorion to be constituted of a variable number of 

 layers, it was because they had never separated it from the mem- 

 branacaduca; but I do not understand how MM. Chevreul, May- 

 grier and Dutrochet could have ever reproduced this old notion. 



At a fortnight, and at three weeks, as well as at two months, the 

 chorion in the human subject is simple, and although, at a later 

 period, other laminae become connected with it they belong to bo- 

 dies not as yet described, and which cannot, under any pretext, be 

 considered as its appendages. 



419. Hippocrates has pretended that the membranes of the foetus 

 arise from the umbilicus. Harvey has said that the chorion, the 

 amnios and chord, are merely prolongations of the child's belly; and 

 Burton, defending the same opinion, expresses himself still more 

 positively on this subject. I myself related some cases, in 1824, in 

 support of such an hypothesis. At the same time an Italian anato- 

 mist, M. Mondini, contributed to strengthen it by means of some 

 particular researches and reasonings. M. Moux states that the 

 chorion, after investing the chord, is continuous with the derm of the 

 foetus. It should be remarked that M. Chevreul is of the same opi 

 nion. Finally, M, Blainville seems to have held a similar opinion. 



But the chorion constitutes a part of the ovule at the moment of 

 fecundation; the abdominal parietes are not developed until after 

 the spine; the chorion presents the same characters and form before 

 the appearance of the skin that it exhibits afterwards; the chorion 

 and the skin are therefore two parts quite independent of each other. 



430. The chorion can be referred neither to the derm, the mus- 

 cles, the aponeuroses, nor peritoneum; however, it is difficnlt to call 

 in question its cellular nature, or to deny its analogy with the 

 serous membranes, of which, besides, it presents all the characters. 



