OF THE SEBOUS SPLANCHNIC MEMBRANES. 177 



folds open, spread out, and are applied to the organs, and then 

 when the latter recede to their original condition, the mem- 

 brane becomes foreign to them; this is owing to the laxity of 

 the sub-serous cellular tissue, near the adhering edge of these 

 folds. When a hernia is produced in the groin and increases 

 in size, it is chiefly by the displacement, the sliding of the 

 serous membrane, assisted by the laxity of the adhesions, that 

 the sac increases; when, on the contrary, an umbilical hernia 

 augments in volume, it is by thinning and distention, that the 

 sac increases, the adhesion of the peritoneum about the umbi- 

 licus being intimate. Bichat has, perhaps, exaggerated a little 

 the influence which the laxity of the adhesions of the serous 

 membranes, may have in limiting their diseases and those of 

 the subjacent parts. 



229. The physical properties of these membranes are. 

 those of the serous system in general already described: they 

 are thin, but this tenuity is not the same in all, neither is it so 

 in all parts of the same membrane, nor in different individuals. 

 Soft, semi-transparent, &c.; their extensibility is strongly 

 marked, more so than that of the synovial membranes; their 

 strength tolerably great, and much greater than that of the 

 cellular tissue; they are slightly elastic. When these mem- 

 branes are distended beyond a certain degree, their texture 

 becomes loose; this looseness is on the free surface; the rest 

 of the thickness of the membranes, resists the laceration more 

 strongly, or yields more to the distention. 



230. They all consist of one lamina, which is so much 

 the more dense and close, if examined on the free surface, and 

 whose texture is more lax on the opposite side where it be- 

 comes flaky and is confounded with the common cellular tissue. 

 Until the period when Douglass gave an exact description of 

 the peritoneum, this membrane as well as those of the same 

 species was considered as bifoliate, and containing the viscera 

 in the space between their separated layers: it was an error 

 which he refuted, and that Vacca and others have vainly tried 

 to revive. The pretended external leaflet is nothing more 

 than the sub-serous cellular tissue, so well described by Doug- 

 lass. They consist essentially of one layer of extremely close 



