UMBILICAL VESICLE, 169 



seventh week, it generally ceases to diminish, but becomes flattened 

 and then insensibly disappears; sometimes it can no longer be found 

 at the third month, while in other cases it may be met with in abor- 

 tions of four, five or six months. 



440. It is incontestably situated betwixt the chorion and amnios. 

 If I maintained a contrary opinion in 1824, it was because I then 

 confounded it with a vesicular body which to a certain extent re- 

 sembles it, but which in fact differs very widely from it, as I shall 

 have occasion to show in the sequel. 



441. Until the fortieth or fiflieth day it is enclosed in the reticu- 

 lated body or vitriform layer; after that it unites with, and applies 

 itself either to the internal surface of the chorion or to the outer sur- 

 face of the amnios. It would seem then that one of these membranes 

 encloses it betwixt its layers; indeed it is most frequendy met with 

 thus, though I have found it peifectly free in ova of two and even 

 three months. 



442. The characters of the pedicle by which it is attached to the 

 embryo vary according to the stage of the pregnancy; until the 

 end of the first month, and in the natural state, I have not found it 

 less than two, nor more than six lines long; at this period of its de- 

 velopment it is often a quarter of a line thick, and in becoming 

 confounded with the vesicle undergoes a sort of infundibuliform ex- 

 pansion. Towards the abdomen it does not enlarge, neither does 

 it contract in any sensible degree. Its continuity with the intestinal 

 tube can now no longer be called in question in the Jiuman subject. 

 Before the parieles of the abdomen are completely formed, it is 

 divided, as it were into two portions by the amnios, which it appears 

 to have traversed or perforated. One of these portions is found 

 betwixt the spine and the spot to be subsequently occupied by the 

 umbilicus; the other remains without, between the amnios and the 

 vesicle. 



443. After the first month the canal elongates, becomes more 

 and more delicate; its umbilical portion is lost in the cord, and can 

 no more be traced as far as the belly; its length may extend to half 

 an inch, an inch or even one inch and a half. Whenever I liave 

 found the vesicle further than this from the root of the cord, it mani- 

 festly depended upon its pedicle havuig been broken by the trac- 

 tions naturally exercised upon it by the membranes when these 

 parts acquire an early and pretty strong adherence to each other. 

 Accordingly as this rupture is effected earlier or later, as the adhe- 

 sions are stronger or weaker, as the pregnancy is more or less 

 advanced, the vitelline sac is found to be more or less remote from 

 the umbilical cord, or if you please, more or less approximated to 

 the circumference of the placenta. 



