OP THE SEROUS SPLANCHNIC MEMBRANES. 175 



has already in a great measure explained the species of which 

 we are now speaking, and which may be considered as the 

 type of the genus. Their form is the same as that of all the 

 serous membranes, that of a bladder without an opening, and 

 with contiguous parietes. On the one hand, it lines the inter- 

 nal surface of the parietes of the cavity in which they are con- 

 tained, and on the other, it furnishes tunicks or external en- 

 velopes to the organs. The pleura, the pericardium, and tu- 

 nica vaginalis have a tolerably simple conformation, their pa- 

 rietal and visceral portions, continuing around the point where 

 the organ they invest is attached by vascular prolongations, 

 to the parietes of the cavity that contains it. As to the arach- 

 noid and peritoneum, their disposition is a little more com- 

 plex, without, however, ceasing to be essentially the same. 

 With respect to the first, the complication is owing to the 

 great number of vessels and nerves that terminate in, or de- 

 part from the brain. Now on each of these parts, the arach- 

 noid forms a sheath, which continues to one of its extremities 

 with the visceral lamina of the membrane, and to the other, 

 with its parietal lamina, an arrangement, previously pointed out 

 and figured by Bonn, to which Bichat has particularly drawn 

 our attention, and from which it results, on the one hand, that 

 the membranous cavity is not open, and that the parts of the 

 membranes are continuous to one another. As to the perito- 

 neum, its complexity depends upon the great number of parts 

 to which it furnishes coverings, and upon the various disposi- 

 tion of these parts, of which some are very near the posterior 

 wall of the abdomen, whence they receive their vessels, and 

 are simply covered with the peritoneum; others again are re- 

 moved from it, sometimes greatly so, and are suspended to 

 membranous bridles which contain the vessels in their thick- 

 ness. Its complexity depends also upon vascular prolonga- 

 tions, projecting beyond the viscera, and to which the serous 

 membrane furnishes epiploical or floating envelopes. This 

 membrane is peculiar also in being the only one that has an 

 opening communicating externally through the fimbriated bo- 

 dy, and fallopian tubes. More extensive details on the con- 

 formation of the splanchnic serous membranes, belong to the 

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