On the structure of the .secreting organs in :,ee the works of Malpighi and of Ruysch; Bichat's Tratee des ilrembranes, and his ?inatomie Generale, tem. i. and iv ; ilorocti's Recherches 4110611W/ Ue8 sac la Posi tion et l'..1ction des Glandes, and his /?c cher( heri sur lc Tz.sszi Illugaeux ; and for the best of the organs treated of in this chapter, see Wmslow's Traite (1%dt:caw/lie ; pa eta of Cu vie r' d'./Inato nzie Comparee, and ol Biehat's _Inutomie De.s.crOtive ; Glisson's ./.1natomia Ileputis ; Satuider's Treatise on the Structure and Economy rf the Liver ; and a paper On the ,Vdeen, by Mr Everard Home, in the Philosophical Tramsactions lo• 1807.
We have now examined all the organs that are con tained within the belly ; but it will be prop r, before concluding this chapter, to give a general view of the form, boundaries, and divisions of this cavity, and to de scribe the disposition and reflections of the serous mem brane by which it is lined.
The abdomen, or belly, is considerably larger than the chest, and is much longer on its sternal than its dorsal side. It is bounded atlantad by the diaphragm, •acra(' by the pelvis, sternud by the recti abdominis mus cles; dorsal by the lumbar vertebra and the muscles that are attached to them, especially the quadrati lumbo rum. On the sides the cat ity is bounded chiefly by the obliejzzi externi, obliyui interni, and transversi abdominis muscles. On the sternal aspect, between the two recti muscles, runs what anatomists call the Linea alba. The belly is usually divided into several parts, called regions, which have received various names, according to their situation, or the parts near which they lie. Dividing the belly from the sternum to the pubis, there are count ed three regions, which we may call atluntal, middle, and sacral regions ; the first beginning at the ensiform carti lage of the sternum, and extending to about a hand's breadth atlantad of the navel, the last from about the same distance &acrad of the navel, or from an imaginary line drawn between the atlanto-sternal spinous processes of time haunch-bones to the pubes, while the middle oc cupies the intermediate space.
Each of these larger regions has been subdivided into three. The atianta/ region has the epigastric in its middle and the right and left hypochondriac regions on its sides; the middle region has the umbilical region for some distance on each side of the navel, and its sides are called the lumbar regions ; and the sacral region has the pogastrie in its middle, arid the right and left iliac regions on its sides.
It will be seen that these regions are extremely arbi trary, and their limits by no means well defined ; but as they arc employed by anatomists in marking the relative situations of the abdominal viscera, we could not proper ly' Omit them.
The peritoneum, cr that membrane which lines the sides of the belly, and is reflected over the most of its contents, ranks, as we have seen, among the serous mem branes. It is thin, and when separated from its attach ments, transparent, though while connected with them, it appears of a whitish colour. It is exceedingly dilata ble, and very elastic. It is supplied with blood-vessels front the small arteries of the parts which it invests; has a few small nervous filaments, chiefly from the great sympathetic and sacral nerves, and numerous absorbents, which pass chiefly to the iliac and lumbar plexuses.
It is not easy to convey in words a just idea of the dis position of this membrane. We have heard it compared to a large thin sheet that we may suppose united at its edges and applied by one part to the linca alba, at the sternal part of the belly, whence it extends on each side, lining all the abdominal muscles, covering the pelvis, passing over the fundus of the urinary bladder, between it and the rectum, while at the atlantal part of the belly it inve,Its the concave surface of the diaphragm, and on the dorsal side passes across towards the vertebra ste• nail of the kidneys. It may be supposed that there is still a great part of the sheet unattached, and that this is wrapped round the liver, the stomach, the spleen, the colon, the small intestines, in such a manner as to follow all their curvatures, and all their convolutions, and to leave doublings between them, forming the omentrim, the mesentery, the mesocolon, and the ineson.ctum, beside the several ligaments that unite many of these viscera to the adjacent organs. Thus, the whole peritoneum is considered as a close bag, one side of which is smooth and equal, and lines nearly the whole cavity of the belly, while the other side is wrapt in innumerable !hidings over the abdominal viscera. I knee it has been remarked, that these viscera do not properly lie within the cavity of the belly, or at least that they are situated behind the cavity formed by the peritoneum.