Front the other side of the root of the me sentery, namely, that which looks upwards and to the right, we may trace the continuity of peritoneal surface off to the right lumbar region, investing the ascending colon in a like, and similarly variable, manner to that in which it was described as investing the descending co lon ; and to the right iliac fossa, where it invests the ccecum, sometimes, but not most frequently, forming a narrow mesentery for it called the meso-ccecum. A bit of mesentery is usually afforded to the vermiform process, but this, of course, we do not reach by proceeding off late rally from the last-mentioned aspect of the root of the mesentery.
As mentioned above, the peritoneum extends across from the front of the rectum to the back of the bladder, in the male subject; the level at which it does so varies with the state of full ness or emptiness of the bladder, and also is said to vary, cteris paribus, in different indi viduals ; frequently it is so low that the peri toneum, passing across touches the prostate. This is in the middle, between the front of the rectum and back of the bladder, but laterally the peritoneum is elevated into two antero posterior folds, which extend across from the sides of the rectum to the sides of the bladder ; these are called the recto-vesical folds or pos terior ligaments of the bladder : anterior and external to them there are two other small folds. External to the recto-vesical folds the peritoneum does not descend nearly so low as it does between them; and therefore there is a remarkable, deepish, cul-de-sac, of the same breadth as the rectum, between that intestine and the bladder.
The posterior and lateral aspects and fundus of the bladder are invested with peritoneum, but not its anterior aspect : the peritoneum passes from the fundus of the bladder, by an even slant, on to the anterior abdominal pari etes, not making any dip in front of it except when it is much distended. In the female there is a deep cul-de-sac of peritoneum be tween the rectum and uterus, descending low enough to be in contact with the vagina : between the uterus and bladder there is a second but much shallower cul-de-sac.
We have now traced the peritoneum over the ascending and descending portions of the colon to the abdominal parietes in the right and left lumbar region ; from the recto-vesical folds and sides of the bladder to the iliac fossze ; and from the fundus of the bladder to the anterior abdominal parietes of the hypo gastric region ; from all or any of these posi tions, or from any point between them, we may trace the peritoneal free surface uninter ruptedly' up to our first starting point, the navel and falciform ligament of the liver.
From the last-named position we have before reached the anterior and posterior surfaces of the lesser omentum, the fortner by tracing the free surface over the left lobe, and the latter by tracing it over the right lobe, of the liver. From the sides of the falciform hepatic liga ment, proceeding in each lateral direction, in a horizontal sectional line taken at the level of the foramen of \Winslow, to the left we find the free peritoneal surface continuing, uninter rupted by any folds, to the external surface of die gastro-splenic omentum in the left hypo cliondriac region ; to the right we find it conti nuing uninterrupted through the foramen of Winslow, covering its posterior boundary, to the internal surface of this same gastro-splenic omentum : to witness its continuity, however, up to the latter point, it is of course necessary to cut through the lesser omentum—in the human subject, but not in those animals which have no foramen of Winslow. ( Figs. 489, 490.) We have now examined the continuity of the peritoneum in all the main directions, and the mode in which it is maintained over the principal viscera and along the connecting sheets with two free surfaces. There yet re main for examination several folds and other remarkable arrangements of this membrane ; the description of these is most conveniently deferred till we come to the consideration of our other propositions, when much that is at present wanting in order to render our proof of the continuity of the peritoneum throughout complete, will be supplied.
The peritoneal cavity is one cavity, in the same sense as the whole of the interior of an hour-glass is one cavity ; that is to say, it is two large cavities made one by being connected by an extremely narrow communicating neck. Supposing the whole of the peritoneal sac could be detached from the connections of its external surface and expanded, it would be a sac of exceedingly irregular figure, divided into two parts by an extremely narrow constriction.