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abdomen and certain other cavities, is to facilitate the movements of the contained viscera during any changes in size or form which they or their containing cavity may undergo. As a result of this arrangement, notwithstanding the tonic pressure of the abdominal wall on its contents, the stomach and intestines are free to move with the greatest ease and the least degree of friction, when any change takes place either in the organs themselves or in their surroundings.
The peritoneum is a thin glistening membrane, which may aptly be compared to a coat of varnish applied to the inner aspect of the abdominal walls, and to the surface of the contained viscera, except where these are directly applied ligament to the walls or to one another. forms throughout its entire extent a continuous and distinct sheet, but it is united so intimately to the viscera, and follows the irregularities of their walls so closely, that it at appears first sight to be a superficial layer of these walls, rather than a separate membrane. Outside the peritoneum lies the tela subserosaalready describedby which the peritoneum is connected more or less intimately to the fascial lining of the abdominal walls and to the abdominal viscera.
The portion of peritoneum which lines the walls of the cavity is known as the peritoneum parietale and that which clothes the viscera as the peritoneum viscerale.
FIG. 915.-DIAGRAMMATIC TRANSVERSE SECTIONS OF ABDOMEN, to show the peritoneum on transverse tracing. A, at level of foramen epiploicum; B, lower down. In A note, one of the short gastric arteries passing to the stomach between the layers of the gastro-lienal ligament, and also the foramen epiploicum leading into the bursa omentalis which lies behind the stomach.
If we trace the peritoneum, beginning in front, we find that it lines the deep surface of the anterior abdominal wall, and is continued upwards to the inferior surface of the diaphragm (Fig. 914), the greater portion of which it covers. From the posterior part of the diaphragmn it is reflected or carried forwards on to the superior surface of the liver. From the liver it can be traced over the stomach, intestines, and other abdominal viscera to the pelvis. In like manner, when traced laterally from the anterior wall, the membrane will be found to line the sides of the cavity, and passing backwards to clothe the posterior abdominal wall, and the
viscera lying upon it (Fig. 914). It should be pointed out that all the abdominal viscera are either directly fixed by connective tissue to the posterior abdominal wall, or connected by blood-vessels with it. In the former case the peritoneum is reflected directly from the wall on to the viscera; in the latter it runs along the blood-vessels to reach the viscera, which it clothes, and then returns to the wall on the opposite sides of the vessels, which it thus encloses in a fold.
Whilst the greater part of the general peritoneal cavity lies anterior to the various abdominal viscera, covering them over and dipping down between them, it should be mentioned that there is a special diverticulum derived from it, situated mainly behind the stomach, and covering its posterior surface; this is known as the bursa omentalis (O.T. small sac), and it will be described in detail later. The aperture through which one sac communicates with the other is termed the foramen epiploicum (Winslowi) (O.T. foramen of Winslow).
In passing from organ to organ, or from these to the abdominal wall, the peritoneum forms numerous folds, the principal ones being as follows:
(1) Omentum Majus.-The greater omentum hangs down like an apron from the transverse colon, in front of the coils of the jejunum and ileum. It consists embryologically of four layers of peritoneum, two anterior and two posterior, which are usually, in the adult, adherent to one another. The four layers form a thin, translucent, and often perforated membrane. The anterior two layers were originally connected with the stomach above, and passed down in front of the transverse colon, but as development proceeds they become adherent to the anterior surface of the transverse colon. The fold which extends from the stomach to the colon is termed the gastro-colic ligament. If the anterior two layers are separated from the posterior two and from the front of the transverse colon, a cavity is formed, continuous with the bursa omentalis, and the anterior layers of the greater omentum are directly continuous with the layers of the gastro-colic ligament. This condition is that usually described in English text-books as the normal adult condition and is represented in Fig. 914, where the gastro-colic ligament is separated from the transverse colon, and passes in front of the transverse colon directly into the anterior layers of the omentum majus, and the great omentum thus descends from the stomach above.
(2) Omentum Minus.—The lesser omentum is a fold passing from the inferior surface of the liver to adjacent organs. It consists of two, or occasionally three. portions:
(a) The ligamentum hepatogastricum, a wide peritoneal fold, extending from the left end of the porta hepatis, the fossa of the ductus venosus, and partly also from the concave surface of the left lobe of the liver and the caudate process, to the lesser curvature of the stomach, where it is continued into the peritoneal coats of the anterior and posterior surfaces of that organ.
(b) The ligamentum hepatoduodenale passes from the porta hepatis to the pars superior of the duodenum. On the left this fold is continuous with the hepatogastric ligament, on the right it ends in a rounded margin. Traced downwards, the layers of peritoneum which form it clothe the commencement of the duodenum on two sides, and are continued into the transverse mesocolon, and into the duodeno-renal ligament.
(c) The ligamentum hepatocolicum is an occasional fold passing from the region of the gall-bladder to the transverse colon and right colic flexure.
(3) Ligamentum Gastrolienale. The gastro-splenic ligament (O.T. gastro-splenic omentum) is a double layer of peritoneum extending between the fundus of the stomach and the hilum of the spleen, and continuous below with the gastro-colic ligament.
(4) The ligamentum gastrocolicum extends from the greater curvature of the stomach to the transverse colon. It consists of two layers of peritoneum, continuous above with the layers on the anterior and posterior surfaces of the stomach, and below with the anterior layers of the great omentum.
In English text-books this is not usually recognised as a separate ligament, but is considered to be a portion of the greater omentum, and to pass downwards in front of the transverse colon. It will be found, however, that the arrangement in the adult is usually that described above.
Mesenteries are folds of peritoneum which unite portions of the intestine to the posterior abdominal wall, and convey to them their vessels and nerves. There are several mesenteries, e.g. the mesenterium (mesentery proper), which connects the jejunum and ileum to the posterior abdominal wall, the mesocolon transversum (transverse mesocolon), the mesocolon pelvinum (pelvic mesocolon), and occasionally others.
Other folds, specially named, but described elsewhere, are the ligaments of the liver, the so-called "false ligaments" of the bladder, the lieno-renal ligament, and the broad ligaments of the uterus.
The stomach is the large dilatation found on the digestive tube immediately after it enters the abdomen (Figs. 916 and 920). It constitutes a receptacle in which the food accumulates after its passage through the oesophagus, and in it take place some of the earlier processes of digestion, resulting in the conversion of the food into a viscid soup-like mixture, known as chyme. The chyme as it is formed is allowed to escape intermittently through the pylorus, into the small intestine, where the digestive processes are continued.
The form and the position of the stomach present great variations, not only among different individuals, but also in the same individual at different times. The degree to which it is filled, the size and position of adjacent organs, the condition of the abdominal walls, and even the assumption of the erect or the recumbent attitude can influence its shape and relations.
Of recent years, examination of the stomach by X-rays has afforded information, otherwise unattainable, of the shape and position of the stomach in life, and of the changes which it undergoes. The results obtained by this method have considerably modified current conceptions regarding the stomach in the living. A necessary preliminary to the proper comprehension of these appearances is a careful study of the stomach as it presents itself to anatomical examination.
General Shape and Position.-In shape, the stomach may be described as an irregularly piriform or conical organ, with a wide end directed upwards and backwards, lying deeply in the hollow of the diaphragm, mainly in the left hypochondriac region, and a narrow tapering extremity which passes downwards and forwards, and is bent over to the right side, in the epigastric region.
The long axis of the organ forms a spiral curve, directed downwards, anteriorly and to the right, and finally backwards.
The superior end, or fundus, is almost always dome-shaped, and is distended with gas, and its wall is thinner and more flaccid than that of the lower portion, which is thicker and somewhat cylindrical in shape.
The walls of the stomach are composed of an inner thick layer of mucous membrane (tunica mucosa), supported by submucous tissue (tela submucosa), a muscular coat, consisting of three layers, more or less complete, of muscle fibres (tunica muscularis), running in different directions, covered externally by a serous, peritoneal investment (tunica serosa). The special characters of each of these walls will be described later.
The stomach presents the following parts for examination :
Two surfaces, an anterior (paries anterior) directed at the same time forwards and to the left, and a posterior (paries posterior) which looks posteriorly and also to the right. These surfaces meet above and to the right at the lesser curvature, curvatura minor, and below at the greater curvature, curvatura major. At the superior end of the lesser curvature the esophagus enters the stomach, at the oesophageal opening, while at the inferior end the stomach passes into the duodenum at the pylorus. The dome-shaped portion to the left of the oesophagus is the fundus, while the remainder of the stomach is divisible into the body, corpus ventriculi, and the pyloric portion, pars pylorica.
The oesophageal opening is termed the cardia, and the portion of the stomach. adjacent to it the pars cardiaca, while the inferior orifice is termed the pylorus, and the portion of the stomach adjacent to it is the pars pylorica, a dilated portion of
The longitudinal muscular coat
phageal fibres pass into the circular muscular coat. The whitish-coloured stratified squamous epithelium of the oesophagus is continuous with the pinkish-coloured columnar epithelial wall of the stomach, and the junction is marked by a sharp irregular line running round the margin of the opening. The orifice itself is oval or
angular rather than round, being
FIG. 916.-THREE VIEWS OF A STOMACH FIXED BY FORMALIN INJECTION IN SITU. compressed from
C. From above.
side to side.
A. From the front. The orientation of the stomach was determined by the insertion of long pins into it in the sagittal, frontal, and transverse planes. These views show the comparatively of the orifice, the horizontal position of the stomach associated with the horizontal posture of the
They also show the partial division into chambers produced by temporary right margin of
merges with a slight curve into the lesser curvature of the stomach, while on the left side there is a deep notch, the incisura cardiaca, between the inferior end of the oesophagus and the fundus, in which lies a strong projecting ridge of the right crus of the diaphragm.
This notch on the outer surface produces a fold in the interior of the stomach, which may assist in closing the œsophageal opening, and this, with the decussating fibres of the diaphragm, and the strengthened circular fibres of the inferior end of the cesophagus, forms a kind of sphincter for this orifice which serves to prevent regurgitation from the stomach under ordinary condition.
The cardia is very deeply placed, and lies about four inches behind the sternal end of the seventh left costal cartilage, at a point one inch from its junction with the sternum. Posteriorly it corresponds to the level of the eleventh thoracic vertebra.
Owing to the fixation of the oesophagus by its passage through the diaphragm, and the close connexion between the stomach and the diaphragm, near the cardia where the peritoneum is absent, this is the most fixed part of the whole organ. The object of this immobility is evidently to maintain a clear passage for the food entering the stomach.
Pylorus.-The pyloric orifice or pylorus is the aperture by which the stomach communicates with the duodenum. It is placed at the extremity of the pyloric end of the stomach, and its position is indicated upon the surface of the stomach by a slight annular constriction which is most marked at the curvatures.
Its position is also indicated by an arrangement of blood-vessels at the pyloric ring, which is nearly constant. On the peritoneal surface a thick vein passes upwards from the lower side somewhat more than half-way on the anterior surface, and from the upper border a second vein reaches downwards in the same line, nearly, if not quite, meeting the first (W. J. Mayo).
The pyloric constriction marks the junction of stomach and duodenum, and there the various coats of these portions meet with one another. The peritoneal covering of the stomach is continued onwards on to the first part of the duodenum. At the pylorus the muscular fibres have a special arrangement, which is due to the presence of a mechanism for arresting the escape of food from the stomach before it has undergone digestion. The longitudinal fibres of the stomach (stratum longitudinale) are in part continued onwards into the longitudinal fibres of the duodenal coat, but many of them bend inwards into the thickened ring around the opening, where they spread out in diverging bundles, which interlace with the most superficial of the circular fibres, and some of them reach and terminate in the subjacent submucosa.
The circular muscular fibres of the stomach (stratum circulare) are not continuous directly with those of the duodenum. On the contrary, at the orifice they become very much increased in number, and they form a thick ring, or sphincter, which is separated from the circular muscular coat of the duodenum by a fibrous septum.
The length of this sphincteric ring is not easily estimated, for while it is sharply marked off from the duodenum there is no sharp line of demarcation on the gastric side. There the ring gradually merges into the circular muscular coat of the cylindrical pyloric canal.
When the pyloric canal is contracted, its wall is nearly as thick as the sphincteric ring.
The gastric mucous membrane (tunica muscosa) is continued into the mucous membrane of the duodenum at the distal margin of the sphincter. The junction cannot be recognised by superficial inspection. The gastric mucosa is considerably thickened where it covers the sphincter muscle. When examined post-mortem in the ordinary way, the aperture, viewed from the duodenal side, is somewhat oval in form. When seen from the opposite side, it presents an irregular or stellate appearance, owing to the fact that the ruga of the gastric mucous membrane are continued up to the orifice.
The orifice is directed horizontally backwards, and to the right. When the stomach is full, however, it looks almost directly backwards, or even slightly to the left side.