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always be distinguished, and are found to bear the same relation to one another as in the dried condition, although this may be obscured by foldings or ruga. The aperture may be slit-like or rounded, with sloping or funnel-shaped edges; the frenula are not so prominent at times; but the whole valve projects much more abruptly into the cavity of the cæcum than in the distended and dried specimen.
Structure of the Valvula Coli.-Each labium of the valve is formed of an infolding of all the coats of the gut, except the peritoneum and the longitudinal muscular fibres, and consequently consists of two layers of mucous membrane, with the submucosa and the circular muscular fibres between, all of which are continuous with those of the ileum on the one hand and of the large intestine on the other. The surface of each labium turned towards the small intestine is covered with villi, and conforms in the structure of its mucous membrane to that of the ileum; whilst the mucous membrane of the opposite surface resembles the mucous coat of the large bowel.
In the dried specimen the superior labium usually projects further into the cavity of the cæcum than the inferior, so that the aperture appears to be placed between the edge of the inferior segment and the inferior surface of the superior.
There is little doubt that the efficiency of the valvula coli is largely due to the oblique manner in which the ileum enters or invaginates the large intestine; this oblique passage alone, as in the case of the ureter piercing the wall of the bladder, would probably be sufficient to prevent a return of the cæcal contents. In the great majority of cases, when in position within the body, the ileum is perfectly protected from
LONGITUDINAL MUSC. FIBRES
such a return, although when the parts are removed, and then FIG. 953.-DIAGRAMMATIC SECTION distended with fluid, this fluid often passes through the valve, and reaches the small intestine. Still, the efficiency of such a test, applied when the parts are deprived of their natural supports, cannot be relied upon.
THROUGH THE JUNCTION OF THE
The size of the segments of the valve, as seen in the dried condition, varies considerably; they are sometimes very imperfect; and even the absence of both has been recorded. But here again there is danger of falling into error, through examining the parts under such artificial conditions.
Types of Cæcum.-Three chief types of cæcum may be distinguished-the fatal type, conical in shape and nearly symmetrical, with the inferior end gradually passing into the vermiform process; the infantile, in which the passage from the cæcum to the vermiform process becomes more abrupt, the lateral wall more prominent, and the whole sac more asymmetrical; and the lopsided adult form, as described above, which is the condition found in 93 or 94 per cent. of adults.
Structure. Nothing in the arrangement of the mucous and submucous coats calls for special notice. The taniæ or longitudinal bands of the muscular coat all spring from the base of the vermiform process (Fig. 954); the anterior runs up on the front, medial to the main prominence of the cæcum; the postero-lateral runs up behind this prominence; whilst the postero-medial passes directly upwards behind the ileum (Fig. 954). The longitudinal fibres on the superior aspect of the ileum partly join the posteromedial tænia; those on the anterior and posterior aspects join the circular fibres of the large gut.
The serous coat has, in connexion with it, certain folds and fossæ which are described at p. 1218.
Processus Vermiformis (Fig. 954). The vermiform process (O.T. appendix, or vermiform appendix) is a worm-like tubular segment which springs from the medial and posterior part of the cæcum about 1 to 1 inches (2.5 to 3.75 cm.) below the ileo-cæcal orifice. From that point it generally runs in one of three chief directions, namely (1) over the brim, into the pelvis; (2) upwards behind the cæcum; or (3) upwards and medially, thus pointing towards the spleen; each of which has been considered to be the normal position by one or more observers. In the first of these situations it is quite evident as it hangs over the pelvic brim; in order to expose it in the second, the cæcum must be turned upwards; whilst, in the third. position, it lies behind the end of the ileum and its mesentery, and these must be raised up in order to display it. In addition to the positions just mentioned, it
has been found in almost every possible situation in the abdomen which its length and the extent of its mesentery would allow it to attain. In every case the anterior tænia of the cæcum, which is always distinct, offers the surest guide to the vermiform process, and its base can be located with certainty by following this tænia to the back of the cæcum (Fig. 954).
Its size is almost as variable as its position. Taking the average of numerous measurements, its length may be given as about 3 inches (92 mm., Berry), and its breadth as inch (6 mm., Berry). On the other hand, it has been found as long as 9 inches (230 mm.), and as short as inch (18 mm.). Even its absence has been recorded (Fawcett), but this must be looked upon as an extremely rare
Its lumen or cavity is variable in its development, and is found to be totally or partially occluded in at least one-fourth of all adult and old bodies examined. This is looked upon as a sign of degeneracy in the process of gradual oblitera tion, which it is by many considered to be undergoing, in the human species. It opens into the cavity of the cæcum on its medial, or medial and posterior aspect
FIG. 954.-THE BLOOD-SUPPLY OF THE CECUM AND VERMIFORM PROCESS.
The illustration to the left gives a front view; in that to the right the cæcum is viewed from behind. In the latter the artery of the process, and three tænia coli springing from the base of the vermiform process should be specially noted. (Modified from Jonnesco).
(Fig. 952), at a point 1 to 1 inches (2.5 to 3.8 cm.) below, and somewhat posterior to the ileo-cæcal orifice. These are the relative positions of the two orifices, as seen from the interior of the cæcum; viewed from the exterior, the base of the vermiform process is within inch of the lower border of the ileum. This apparent difference is due to the fact that the ileum adheres to the medial side of the cæcum for a distance of nearly 1 inch before it opens into it.
Sometimes the orifice of the vermiform process has a crescentic fold or valve. the valvula processus vermiformis, placed at its superior border; but it is probably of very little functional importance, for the aperture of the process is usually so small that its cavity is not likely to be invaded by the contents of the cæcum.
The vermiform process is completely covered with peritoneum, and has a considerable mesentery, the mesenteriolum processus vermiformis (O.T. meso-appendix) which extends to its tip as a rule, and connects the process to the inferior surface of that part of the mesentery proper which goes to the inferior extremity of the ileum.
The vermiform process is relatively, to the rest of the large intestine, longer in the child at birth than in the adult, the proportion being about 1 to 16 or 17 at birth and 1 to 19 or 20 in the adult. (The difference is certainly not as great as stated by Ribbert, who makes the proportion 1 to 10 at birth and 1 to 20 in the adult.) The process attains its greatest length and diameter during adult and middle age, and atrophies slowly after that time. slightly longer in the male than in the female.
It is said to be
Total occlusion of its cavity is found in 3 or 4 per cent. of bodies; it is then converted into a fibrous cord. Partial occlusion is present in 25 per cent. of all cases, and in more than 50 per cent.
of those over 60 years old, whilst it is unknown in the child. This frequency of occlusion, the physiological atrophy which takes place after middle life, the great variations in length, and other signs of instability, have been considered to point to the retrogressive character of the vermiform
A vermiform process is found only in man, the higher apes, and the wombat, although in certain rodents a somewhat similar arrangement exists. In carnivorous animals the cæcum is very slightly developed; in herbivorous animals (with a simple stomach) it is, as a rule, extremely large. It has been suggested that the vermiform process in man is the degenerated remains of the herbivorous cæcum, which has been replaced by the carnivorous form. Another and perhaps more probable view regards the process as a lymph organ, having the same functions as lymph I nodules, and, like these, undergoing degeneration after middle life (Berry).
In the foetus and child, as well as in the adult with the infantile type of cæcum, the vermiform process springs from the true apex, not from the medial and posterior aspect.
It will be observed that the tela submucosa is almost entirely occupied by lymph nodules and patches. The lamina muscularis mucose is very faint, and lies quite close to the bases of the intestinal glands. The longitudinal layer of muscular fibres forms a continuous sheet.
Foreign bodies, although reputed to find their way very easily into the vermiform process, are rarely found there after death. On the other hand, concretions or calculi, formed of mucus, fæces, and various salts, are often present (Berry).
Structure (Fig. 955). The tunica serosa is complete, and forms a perfect investment for the process. The tunica muscularis, unlike that of the rest of the large intestine, has a continuous and stout layer of longitudinal fibres, which passes at the root of the process into the three tæniæ coli (Fig. 954). The layer of circular fibres is well developed. The tela submucosa is almost entirely occupied by large masses of lymph tissue surrounded by sinus-like lymph spaces. Owing to the large size of these lymph nodules, the areolar tissue of the submucosa is compressed against the inner surface of the muscular coat, and forms a well-marked fibrous ring, which sends processes at intervals between the lymph masses towards the mucous membrane. These lymph nodules, which correspond to solitary lymphoid nodules, have, owing to their great number, been almost completely crushed out of the mucosa (in which they chiefly lie in the intestine) into the submucosa. The mucous coat corresponds to that of the large intestine in its general characters, but the intestinal glands are fewer, and irregular in their direction; the lamina muscularis mucosa is thin and ill-defined; it lies just internal to the lymphoid nodules of the submucosa, and immediately outside the base of the intestinal glands. Some few lymph
nodules lie in the mucous coat also.
Blood-vessels of the Cæcum and Vermiform Process (Fig. 954). These parts are supplied with blood by the ileo-colic artery. This gives off, near the upper angle formed by the junction of the ileum with the small intestine-(a) an anterior ileo-cocal artery, which passes down on the front of the ileo-cæcal junction to the cæcum, and breaks up into numerous branches for the supply of that part; (b) a posterior ileo-cæcal artery, similarly disposed on the back; and (c) the artery for the vermiform process. The last-named branch passes down behind the ileum (Fig. 954), then enters the mesentery of the process, and running along this near its free border, sends off several branches across the little mesentery to the process, before finally ending in it. The course of the artery behind the ileun is said to render it subject to pressure from fæcal masses in that gut, and thus to predispose to an interference with the blood supply of the vermiform process, and to morbid changes in it.
The lymph vessels of the cæcum and vermiform process arise mainly from networks in the mucous and serous coats.
The first of these networks communicates with a lymph sinus which is found at the base of the lymph nodules in the process, and the vessels from it pierce the muscular coats, and pass in company with the blood-vessels. They are connected with mucous lymph glands found near the ileo-cæcal junction, especially on the posterior and medial aspect, in the angle between the
ileum and colon.
Small isolated glands may be found lying in close contact with the medial part of the cæcum on its anterior and posterior aspects. From these glands, the lymph stream is directed upwards and medially towards the coeliac and lumbar glands. The lymph vessels of the vermiform process may also communicate with the lymph nodes in the iliac fossa, and also, it has been stated, with the lymph vessels of the right ovary.
Cæcal Folds and Fossæ.-The peritoneum in the neighbourhood of the cacum forms certain fossæ, of which the most interesting and important are (a) the fossa cæcalis; (b) the recessus ileocæcalis inferior; (c) the recessus ileocæcalis superior; and (d) the recessus retrocæcalis.
(a) The fossa cæcalis (Fig. 956, B) is only occasionally present, and can be exposed by turning the cæcum and adjacent part of the ileum upwards. It is a fossa in the
In A, the cæcum is viewed from the front; the mesentery of the vermiform process is distinct, and is attached above to the inferior surface of the portion of the mesentery going to the end of the ileum. In B, the cæcum is turned upwards to show a retro-cæcal fossa, which lies behind it and behind the beginning of the ascending colon.
parietal peritoneum on the posterior abdominal wall, open above, in which the lower end of the cæcum occasionally lies. It is produced by the plica cæcalis, a peritoneal fold which passes from the surface of the iliacus to the right lateral aspect of the cæcum. Two forms, lateral and medial, are described; the first lies behind the lateral part of the ascending colon, immediately above the cæcum; the second behind its medial part. These fosse are specially interesting because, when present, they frequently lodge the vermiform pro cess (see Fig. 956, B), a condition which is said to favour the production of appendicitis.
(b and c) Recessus Ileocæcales and Plica Ileocæcalis.If the vermiform process drawn down, and the finger run towards the cæcum, along the inferior border of the terminal part of the ileum, its point will generally run into a fossa situated in the angle between the ileum and cæcum (Fig. 956, A), which is known as the recessus ileocecalis inferior. The fold which bounds the fossa in front is the plica ileocacalis (O.T. the "bloodless fold of Treves"). It passes from the ileum to the front of the mesentery of the vermiform process, which forms the posterior wall of the fossa.
The plica ileocæcalis contains some unstriped muscle fibres continuous with the longitudinal muscle coat of the cæcum, and some fat especially at its free margin.
The recessus ileocæcalis inferior is bounded above by the lower end of the ileum, to the right by the cæcum, in front by the plica ileocæcalis, behind by the root of the mesenteriolum of the processus vermiformis, while it is open to the left or medially.
Similarly, if the finger is run out along the superior border of the ileum towards the cæcum, it will usually lodge in a smaller fossa, the recessus ileocæcalis superior, which is
bounded in front by a small peritoneal process, the ileo-colic fold (Fig. 956, A), containing the anterior cæcal artery.
The recessus ileocæcalis superior lies at the upper margin of the opening of the ileum into the colon, and is bounded behind by the ileum, to the right by the
(d) Recessus Retrocæcalis.-This is an occasional recess which passes upwards between the ascending colon and the posterior abdominal wall. Its orifice looks downwards or to
the left, and lies in the fossa cæcalis behind the cæcum.
Colon Ascendens.-The ascending colon begins about the level of the intertubercular plane, opposite the ileo-cæcal orifice, where it is continuous with the cæcum. From there it runs upwards and somewhat posteriorly, with a slight concavity to the left, until it reaches the inferior surface of the liver, where it bends forwards and to the left, and passes into the right flexure of the colon (Fig. 957). In its course it lies in the angle between the quadratus lumborum, and the more prominent psoas major medially (Fig. 957).
It is situated chiefly in the right lumbar region, but it extends slightly into the hypochondrium above; and, although it usually begins about the level of the intertubercular plane, still with a low position of the cæcum it will extend further down, and may occupy a considerable part of the iliac region.
Its length is extremely variable, depending upon the extent to which the cæcum has descended from the position it occupied during development, viz., in contact with the under surface of the liver.
It is from 5 to 8 inches long, and it is wider and more prominent than the descending colon. It generally presents several minor curves or flexures, and it often has the appearance of being pushed into a space which is too short to accommodate it.
Relations.-Anteriorly, it is usually in contact with the abdominal wall, but the small intestine frequently intervenes, particularly above (Fig. 957). To its medial side lie the coils of the small bowel and the psoas major; to the lateral side is the side wall of the abdomen. Its posterior surface, which is free from peritoneum as a rule (Fig. 968), is connected by areolar tissue to the iliacus muscle as far up as the crest of the ilium, to the quadratus lumborum above that, and finally to the inferior part of the right kidney.
In the great majority of cases only the two sides and the anterior surface are covered with peritoneum, the posterior surface being destitute of a serous coat (Fig. 968). In a small proportion of bodies, however, the ascending colon is provided with a complete peritoneal coat and a mesentery, but this latter is so short that it admits of but a slight amount of movement in the gut.
On the lateral aspect of the cæcum and colon there are occasionally found small peritoneal pockets termed recessus paracolici.
Like the cæcum, the ascending colon is frequently found distended with gas or fæces after death, hence in part its large size and prominence as compared with the descending colon, which is generally empty.
Flexura Coli Dextra.-The right (O.T. hepatic) flexure of the colon is the bent piece of the large intestine between the end of the ascending colon and the beginning of the transverse colon (Figs. 947 and 957).
When the ascending colon reaches the inferior surface of the liver, it bends— usually acutely, sometimes obtusely-forwards and to the left on the anterior surface of the right kidney, and on reaching the front of the descending portion of the duodenum, passes into the transverse colon.
The flexure is placed between the descending duodenum medially and the anterior thin margin of the liver, or the side wall of the abdomen, laterally; above, it corresponds to the colic impression on the liver, and posteriorly it rests on the kidney. Its peritoneal relations are similar to those of the ascending colon.
Colon Transversum.-This is the long and looped portion of the large intestine