16S APPENDAGES OF THE FCETUS. 



first its dimensions exceed those of the embryo. Now if it be true that 

 many assertions emitted on this subject are correct, it is not less so, 

 that what M. Lobstein has observed does not prove it to be so; for the 

 ovum of which he has given a drawing being certainly in an unna- 

 tural state, all the data resulting from the examination of such a spe- 

 cimen, can be of no weight in science. 



Another figure of the umbilical vesicle, in the human species, is 

 annexed to M. Meckel's memoir; but it must be that the drawing 

 is a bad representation of the original, or that the original has un- 

 dergone some change, for the vitelline sac, the embryo itself, and its 

 envelops are not commonly disposed in that way at the end of the 

 fourth week. 



Among all the drawings that have been mentioned by authors, 

 without excepting that of M. Dutrochet, I am acquainted with 

 only two that incontestably represent the umbilical vesicle in its na- 

 tural state in the first six or eight weeks of pregnancy; they are 

 those of A^lbinus and Soemmering, and yet much is wanting espe- 

 cially to the former, in a great many respects. 



438. However, the numerous cases I have collected enable me 

 to affirm that the human ovum always contains, until the eighth week 

 of its growth, a vesicle similar or nearly similar to those noticed by 

 Albinus, Scemmering, MM. Meckel, Dutrochet, &c.; that if nu- 

 merous naturalists failed to meet with it, it was because they sought for 

 it in specimens from which it had disappeared, either by the natural 

 progress of pregnancy, or by the rupture of the membranes in the 

 abortion, or in consequence of some morbid state, or the decom- 

 position of the parts that enter into the texture of the ovum, or 

 lastly, because they were not sufficiendy practised in these sorts of 

 researches always to detect it, though it really existed. 



In a total of about one hundred and thirty sp-^cimens, examined 

 before the end of the third month, I only met with the umbilical ve- 

 sicle in a stale that could be called natural, thirty times. I have had 

 drawings made of six of these vesicles, and I still possess some that 

 are pretty well preserved in alcohol. 



439. The umbilical vesicle is a small pyriform sac of a rounded 

 or spheroidal shape, which about the fifteenth or twentieth day after 

 fecundation is as large as a common pea, that is to say from two 

 to four lines in diameter. It probably acquires its greatest dimen- 

 sions in the course of the third or fourth week; at least, I have al- 

 ways found it smaller beyond the first month. I confess I never 

 had an opportunity of examining but one before the first fortnight, 

 and that was also smaller. When reduced to the size of a corian- 

 der seed, which commonly takes place about the fifth, sixth or 



