CONTINUITY OF THE PERI TONEU M.—To demonstrate the unbroken continuity of the peritoneum, we are compelled, in description, to trace it in various directions, starting from a certain point and following it up till, having performed a complete circuit, we return again to our starting point. In doing so we shall avoid restricting ourselves to the mesial or any other sectional line. We believe that such a restriction, closely adhered to, tends to convey an erroneous impression, namely, that of a line instead of a superficial expanse. In thus tracing the peritoneum, it is better to let the mind rest upon the idea of a free surface, rather than upon that of a mem brane. By a membrane one is apt to under stand a separable skin ; but in some situations not only is it impossible, by any ordinary ma nipulation, to separate the peritoneum from its connections, but two layers of it often form together a structure so thin that one can hardly help regarding it as a single membrane. In no instance is any part of a serous membrane free on both its surfaces. The external surface of the peritoneum, like that of all other serous sacs, is every where adherent, either to the sub jacent structures, or, as in its duplications, to itself; whilst, on the other hand, its internal surface is, normally, every where free. It follows then, that wherever, in the peritoneal cavity, the finger can be placed on a free sur face, there is a layer of peritoneum immedi ately beneath it ; that if a continuous free surface is demonstrated, the continuity of the serous membrane is proved ; that in fact a free serous surface represents a layer of serous membrane, and may be described instead of it when continuity alone is sought to be proved. NVe shall therefore at present use the expres sions free surface and layer of serous mem brane as synonymous ; the free surface of a viscus instead of the serous membrane invest ing a viscus.
When the abdominal cavity is laid opPn in front by a crucial incision, the inner surface of the reflected flaps is seen to be free, glistening, and of a pale red colour. By a slight exami nation of the cut edges this is found to be the free surface of a membrane, whereof the other surface is connected to the subjacent structures by areolar tissue : the free surface is the parietal serous surface of the abdomen : the membrane is the parietal portion of the peritoneum. If
an incision has been carried from the navel to the xiphoid cartilage, a falciform, membrane like process, strikingly resembling the frcenum Unglue, is seen connected with the anterior parietal peritoneum, a little to the right of the middle line, projecting backwards, and towards that aspect presenting a free concave border. It is the falciform ligament of tbe liver. The base or broadest extremity of the falx is sessile along an antero-posterior line upon the upper surface and anterior edge of the liver ; which line corresponds with and runs into the great antero-posterior fissure on the under surface of the liver; and this fissure receives the round ligament, and consequently the free edge of the falx which encloses it. The apex of the falx is at a point on the inner surface of the anterior abdominal parietes, corresponding to the navel. The surfaces of the falciform liga ment are continuous with the serous surfaces of the parietes and liver; its free border, as inci dentally mentioned above, encloses a structure called the round ligament of the liver, which gives a considerable thickness to this part.
The round ligarnent of the liver is the umbi lical vein of the fcetus, degenerated to a fibrous cord in the adult, and it runs across, as that vein did, from the navel to the antero-posterior fissure oldie liver, defining the free border of the falciform process in question. The composition, then, of the falciform ligament of the liver is- a portion of peritoneum doubled or folded, so that its outer surface is brought in contact with itself, as happens when a sheet of paper is folded so as to make two leaves. The two surfaces thus brought into contact, are united together by areolar tissue, as if the two leaves were stuck together with paste ; and the round liga ment lies along in the extreme edge of the fold, like a string that holds a sheet of two leaves in a book-cover. The vessels necessary for the nutrition of these structures ramify in the in terposed areolar tissue. It seems as if the umbilical vein, in making the shortest route from the navel to the longitudinal hepatic fis sure, had carried back before it a fold of the superjacent peritoneum.