Throughout the whole of the large intestine, the peritoneum is here and there developed into peculiar, processes, called the appendices epiploicre Cirt,TXDov, omentum). These are short pouches of the serous membrane, which generally form flattened duplicatures or folds. They are prolonged from the peritoneum cover ing the surface of the intestine itself; and are therefore absent from that portion of the rectum, or terminal segment of the large in testine, which does not receive any covering of this membrane. Their number, size, and arrangement, are liable to great variety. Some times they are so numerous, as to form a single or double row along the free surface of the bowel. In other instances they are very few and imperfect. Their size is so far related to the state of the bowel, that, like niost other processes of peritoneum, they are enlarged by its contraction, and dimi nished by its distention. From their con tents, which consist of areolar and adipose tissue, they would seem to be small reser voirs of fatty matter. Hence in cases of re markable obesity, their size is much increased. Indeed they sometimes acquire a length of one or two inches ; and have even been known to encircle and strangulate the bowel.
Movenzent of the large intestine.—The exact nature of the movement which is executed by the muscular coat of the large intestine can at most only be conjectured from some of its attendant circumstances. Like that of the preceding segment of the canal, though its general mechanism is obvious, its details remain unknown.
As regards the investigation of the con tents of this intestine in its ordinary situation during life, all that can be stated is, that, even in health, they include a quantity of gaseous matter.; which usually maps out the ccecum, and more or less of the colon, with tolerable distinctness, from the less resonant convolutions of the small intestine.
After death, the quality and quantity of these contents are so much affected by the nature of the previous food, the mode of dying, and a va riety of kindred causes, that scarcely any gene ral proposition can be laid down with respect to them. But on the whole, we usually find, that in addition to much gaseous fluid, the cwcum of the healthy subject is partially distended by pultaceous or semi-fluid contents. While the colon is occupied at various points of its length by matter, the ficcal character of which is still more distinct, and the consistence of which gradually increases as it approaches the rectum.
IN here these rudimentary fzeces are very im perfect, scanty, and interrupted, they only oc cupy some of the sacculi or cells of the bowel, leaving its central or general calibre in an empty state. But when better developed, they form what is termed a " figured " mass. This con sists of a kind of central rod, that corresponds to the general axis of the tube; and of processes that come off from the sides of this axial por tion, and are contained in the rows of pouches formed by the wall of the bowel. In short, the solid and continuous fmcal substance forms a tolerably perfect cast of the bowel ;—a cast in which the sacculi of the colon are "figured " as projections, themselves isolated by depres sions corresponding to the intersections of its longitudinal and transverse bands.
The characteristic shape thus possessed by the solid contents of the colon, is often retained by the fmces which have been forced through the rectum in the natural process of defmca tion. And although it is often absent,—the con
sistence of the fmces being such* as to mould them to the cylindrical form of the last-named portion of tube through which they have to pass—still it occurs so frequently in Man, and so universally in many- of those Herbivora in hom we can best study the phenomena of a highly developed large intestine, as to afford a valuable testimony to the natural action of this part. It is therefore difficult to avoid believing, that the individual sacculi of the colon, or at least of its later segments, retain the fleces for a considerable period of time ; during which they so far complete the action of the large intestine upon these its contents, as to leave nothing for its remaining segments to effect, save their mechanical propulsion to wards the outlet of the canal. To this inter mittent action of the muscular coat in respect of time, we may probably add a similar inter ruption as regards space. In other words, the interrupted and irregular manner in which the sacculi are often occupied by solid fmces, entitles us to suspect, that different lengths of the intestine can act independently of each other. But it is difficult to hazard a con jecture as to whether the contraction of the falciform transverse folds ever really shuts off portions of the tube into distinct cavities. The central axis of the figured evacuation is, however, often so slender, or even interrupted, as remarkably to corroborate such a view. And some authors have assumed that the cmcum, during its digestive act, is isolated from the ascending colon by a vigorous con traction of that large fold which is prolonged froni the frcena (or anterior and posterior extremities) of the ilio-cmcal The little information afforded us by direct observation on the movements of the intestine, confirms what is thus vaguely suggested by the appearances of its expelled contents. The highly developed large inte.tine of the living or newly-killed rabbit, rarely exhibits any noticeable movement whatever, when first ex posed to the air. By and bye, however, a kind of irregular peristalsis comes on. But this is nowhere quite so energetic as that seen under similar circumstances in the small intestine ; and is generally very feeble in the cmcum.* And in this movement, as in that produced by mere local irritation, we may notice the peculiar character before attributed to the contraction of unstriped muscle generally ;— viz., that of diffitsing itself over a thne and space greater than those occupied by the irritation which has excited it. As regards the details of this vermicular action, certain sacculi contract and dilate alternately ; the transverse constrictions between them shar ing in the same movement. This alternate movement is often accompanied by an irregular contraction of the longitudinal bands; which is sometimes carried to such an extent, as to shorten the tube, by approximating and di lating certain of its cells. And even where the effect of the local irritation survives its cause, so as to excite a continuous movement which proceeds along a considerable length of intes tine, still it rarely affects all the cells of the bowel exactly alike; but often passes lightly over one or two, to bear with increased inten sity on those which immediately succeed them. Very- similar movements are produced by galvanizing the solar plexus which gives off the nerves to the large intestine.