174 APPENDAGES OF THE FCETUS. 



this specimen, that I am not sure of having seen it; besides, as on 

 the one hand the summit of the urinary bladder naturally reaches 

 as far as the umbilicus, and as on the otlier side 1 traced the reticulated 

 sac from the root of the cord as far as the navel, it was impossible 

 to make a nearer approach, without reaching it, or without actually 

 demonstrating it, to render this communication more probable. 



In embryos more advanced, I have many times traced the urachus 

 into the umbilical cord, where it unravels and is transformed into a 

 porous tissue, and terminates either in one of the swellings when 

 they still exist, or in the gelatinous tissue of the placental stem after 

 passing on for six or eight lines, or one inch, or fifteen lines. I have 

 seen more; in an ovum of five or six weeks old, the prolongation 

 from the bladder proceeded to, and was lost in the vitriform layer, 

 which at this period takes the place of the porous body of the ovule; 

 I must however confess, that having blown air into the bladder, I 

 could not make it penetrate into the urachus, which always retained 

 the characters of a solid filament. 



455. From the fifth week after conception until the close of preg- 

 nancy, there is betwixt the chorion and amnios a transparent stra- 

 tum, either colorless or of a somewhat greenish red; this stratum, 

 instead of being merely serous, is lamellated after the manner of the 

 vitreous body; it diminishes in thickness in proportion to the deve- 

 lopment of the other membranes; the quantity of fluid contained in 

 its meshes is, on the contrary, in the inverse ratio of the progress of 

 gestation; by diminishing in thickness, it at length comes to form 

 only a homogeneous pulpy stratum, to transform itself into a simple 

 gelatinous or mucous coating, which, in many women, wholly dis- 

 appears before the period of delivery; several of its lamellae are 

 confounded together at the external surface of the amnios, princi- 

 pally in the environs of the root of the umbilical cord: the same 

 thing takes place, but more rarely as to the chorion, which explains 

 why the umbilical vesicle, observed after the sixth week of gestation, 

 is very often united, as if framed in, with the membranes of the cho- 

 rion and amnios; this matter occupies the place of the reticulated 

 body, and like the latter is continuous with the gelatinous portion of 

 the cord. But is it independent of the porous sac which precedes 

 it; or rather is it only a modification thereof? This last conjecture 

 seems to me, to be, if not certainly true, at least extremely probable. 



456. In order to acquire more enlarged notions concerning the 

 bodies in question, naturalists may advantageously have recourse to 

 comparative anatomy; for I have found betwixt the allantois of ovi- 

 parous reptiles, and the reticulated body of the human ovum, the 

 most exact resemblance. 



