The foramen of Winslow is not generally big enough to admit more than one or two fingers to be passed through it ; but an incision being made through the lesser omentum, the hand may be introduced into the °mental sae and passed downwards behind the stomach and in front of the transverse colon, until it reaches the lowermost extent of the great omentum, or bot tom of the great omental pouch ; it will thus be between the two layers of what we considered like a double apron, but which, rather, is a pouch. The hand may now be carried in either lateral direction until it is arrested by the sides of the pouch, which correspond, on the right with the point where the colon crosses the duo denum, and on the left with the point where the colon, from being transverse, becomes de scending,—that is to say, the sides of the pouch hang doNvn from these points. Above the latter point, the hand may be carried towards the left, beyond the fundus of the stomach and some what behind the spleen, where it will be arrested by an attachment to the posterior parietes, the line of which extends from the cardia to the left bend of the colon.
There is, therefore, a great pouch of perito neum, the inside and outside of which are both free ; and consequently it has an internal or lining layer and an external layer; we will presently show how these are continuous with each other and with the peritoneal investments of surrounding parts. The left side of the mouth of this pouch is carried up into a long corner reaching the cardia ; its continuous line of attachment extends from the cardia along the greater curvature of the stomach to the pylorus ; then along a small extent of the duodenum till it reaches the transverse colon; next along the transverse colon to its left bend, and thence along on the posterior abdominal parietes of the left hypochondriac region, or rather over the left kidney, to the cardia whence we started. The spleen is sessile upon the external surface of this bag to the left of the fundus of the sto mach. That portion of it which intervenes between the stomach and colon is called the great omentum, and that portion which is situated to the left of the fundus of tbe stomach is called the splenic omentum.
We may now return to our demonstration of the continuity of the peritoneum by tracing its free surface as before. The two surfaces or layers of the lesser omentum were seen to be continuous around the vesseLs enclosed in its free right border, at the foramen of Winslow. These two layers, as yet adherent, separate at the lesser gastric curvature, invest the stomach —one behind and the other in the front—meet ag,ain, and again adhere along the fundus and greater curvature, forming a sheet with two free surfaces, which to the right extends to the spleen and abdominal parietes, and downwards to the transverse colon ; that part of it, however, which intervenes between the stomach and colon is bagged out or excessively widened so as, in ordinary circumstances, to hang down in a pouch as low as the pelvis. Having reached the front of the transverse colon, the layers again separate to invest it—one above and the other below—meet again on its posterior aspect, and again adhering together form the transverse me socolon, which extends from the colon to the posterior abdominal parietes, where having ar rived they finally separate, partially investing, as they do so, the transverse portion of the duode num. Thus both layers reach the abdominal parietes along the continuous line of attachment of the splenic omentum and the transverse me socolon ; the internal layer from this continuous line invests the pancreas and other parts behind the stomach, then the lobulus Spigelii, and thus is conducted to the posterior surface of the lesser omentum, from which we started. The
external layer of the omental sac, having reached this line of parietal attachment as part of the splenic omentum to the left, passes off on the left kidney and the lateral abdominal parietes and diaphragm ; having reached it below as the transverse mesocolon, it may thence be traced downwards to the root of the mesentery. The small intestine is enclosed in the extre mity of the fold of a duplicature of peritoneum. That part of the fold which extends across from the posterior parietes to the intestine is called the mesentery. The two component layers of the mesentery are adherent by their apposed surfaces, except where vessels, &c. intervene, so that it is a parieto-visceral sheet with two free surfaces. The parietal attachment of the me sentery is called its root, and extends obliquely across the spine from the left side of the seccud lumbar vertebra, where the duodenum emerging from the root of the transverse mesocolon be comes jejunum, to the right iliac fossa, where the ilium enters the ccecum. Though the pa rietal attachment or root of the mesentery is but a few inches in length, its visceral attachment by means. of numerous ample foldings, like a ruffle, corresponds in length with the twenty feet of small intestine. Tracing, then, the peri toneum heretofore forming the external layer of the great °mental sac from the point where it reaches the posterior parietes as part of the transverse mesocolon, downwards, we come to that side of the root of the mesentery which looks upwards and to the right ; thence we trace this surface continuous along the mesen tery, over the bowel, back again along the other side of the mesentery, so reaching that side of its root whose aspect is downwards and ,to the left ; in both which directions the peritoneum may be traced onwards. To the left it reaches the right side of the descending colon, invests the front of that bowel, and passes off 011 the other side of it to the lateral parietes : occa sionally only does it dip beneath the descending colon so as to come in contact with itself and form a mesentery for it. A little lower down, however, namely, in the left iliac fossa, it always forms a mesentery for the sigmoid flexure of the colon, and, still lower down, for the first part of the rectum. The distinction, however, between iliac mesocolon and mesorectum, as the mesenteries of the sigmoid flexure and rec tum are called, is quite arbitrary and unnatural; a continuous mesenteric duplicature, broad in the middle and tapering to each end, serves to give attachment to both the sigmoid flexure and the first part of the rectum. Proceeding from the root of the rnesentery downwards in the middle line, the peritoneum covers the sacro vertebral protninence, and, just below, it ar rives at the rectum and forms a mesentery for its first portion as above stated. The perito neum invests the front only of the second por tion of the rectum, and at a variable distance from the anus quits it and extends across to the back of the bladder in the male, or vagina and uterus in the female, so that the lowermost por tion of the rectum is destitute altogether of pe ritoneal investment.